Showing papers in "Analytical Methods in 2021"

Comparative study of four greenness assessment tools for selection of greenest analytical method for assay of hyoscine N-butyl bromide

Abstract: Several assessment tools were recently introduced for the evaluation of the greenness of analytical methods. Each tool has advantages, disadvantages, and a unique assessment protocol. The final results obtained from each assessment tool may lead to a dissimilar conclusion about the selection of the greenest method, which makes the decision confusing as to which an assessment tool relies on. Accordingly, in this comparative case study, four greenness assessment tools—National Environmental Methods Index (NEMI), Eco-Scale Assessment (ESA), Green Analytical Procedure Index (GAPI), and Analytical GREEnness metric (AGREE)—were tested to evaluate 16 chromatographic methods described in the literature for the assessment of the commonly used antispasmodic drug Hyoscine N-butyl bromide (HNBB). The importance of applying more than one assessment tool when evaluating the greenness of analytical methods is explained in this study. Despite NEMI tool simplicity, it was the least effective in providing information about the analytical method as 14 out of 16 methods had the same NEMI pictogram. ESA and AGREE provided reliable numerical assessments that differed in their total scores whereas the total scores were out of 100 and 1 for each, respectively. AGREE has the merits over ESA with respect to automation and highlighting the weakest points in analytical techniques that need further improvements in terms of greenness. GAPI and AGREE provide fully descriptive three-colored pictograms. The main disadvantage of GAPI is complexity compared to NEMI and ESA. AGREE has the merits of simplicity and automation over GAPI. Based on the results, recommendations are made for ESA, GAPI, and AGREE tools, which provide reliable and precise results about the greenness of the method. Planning for the greenness of analytical methods should be assured before practical trials in a laboratory for reduction of chemical hazards released into the environment. Moreover, inclusion of the evaluation of greenness of analytical methods in method validation protocols is strongly recommended.

A review of pharmaceutical occurrence and pathways in the aquatic environment in the context of a changing climate and the COVID-19 pandemic.

Abstract: Active pharmaceutical ingredients (APIs) are increasingly being identified as contaminants of emerging concern (CECs). They have potentially detrimental ecological and human health impacts but most are not currently subject to environmental regulation. Addressing the life cycle of these pharmaceuticals plays a significant role in identifying the potential sources and understanding the environmental impact that pharmaceuticals may have in surface waters. The stability and biological activity of these "micro-pollutants" can lead to a pseudo persistence, with ensuing unknown chronic behavioural and health-related effects. Research that investigates pharmaceuticals predominantly focuses on their occurrence and effect within surface water environments. However, this review will help to collate this information with factors that affect their environmental concentration. This review focuses on six pharmaceuticals (clarithromycin, ciprofloxacin, sulfamethoxazole, venlafaxine, gemfibrozil and diclofenac), chosen because they are heavily consumed globally, have poor removal rates in conventional activated sludge wastewater treatment plants (CAS WWTPs), and are persistent in the aquatic environment. Furthermore, these pharmaceuticals are included in numerous published prioritisation studies and/or are on the Water Framework Directive (WFD) "Watch List" or are candidates for the updated Watch List (WL). This review investigates the concentrations seen in European Union (EU) surface waters and examines factors that influence final concentrations prior to release, thus giving a holistic overview on the source of pharmaceutical surface water pollution. A period of 10 years is covered by this review, which includes research from 2009-2020 examining over 100 published studies, and highlighting that pharmaceuticals can pose a severe risk to surface water environments, with each stage of the lifecycle of the pharmaceutical determining its concentration. This review additionally highlights the necessity to improve education surrounding appropriate use, disposal and waste management of pharmaceuticals, while implementing a source directed and end of pipe approach to reduce pharmaceutical occurrence in surface waters.

Developing a systematic method for extraction of microplastics in soils.

Abstract: Microplastics are an environmental issue of global concern. Although they have been found in a range of environments worldwide, their contamination in the terrestrial environment is poorly understood. The lack of standardised methods for their detection and quantification is a major obstacle for determining the risk they pose to soil environments. Here we present a systematic comparison of microplastic extraction methods from soils, taking into account the characteristics of the soil medium to determine the best methods for quantification. The efficiency of organic matter removal using hydrogen peroxide, potassium hydroxide and Fenton's reagent was measured. Soils with a range of particle size distribution and organic matter content were spiked with a variety of microplastic types. Density separation methods using sodium chloride, zinc chloride and canola oil were tested. Recovery efficiencies were calculated and the impact of the reagents on the microplastics was quantified using Attenuated Total Reflectance (ATR) Fourier Transform-Infrared (FTIR) spectroscopy. The optimal organic removal method was found to be hydrogen peroxide. The recovery efficiency of microplastics was variable across polymer types. Overall, canola oil was shown to be the optimal method for density separation, however, efficiency was dependent on the amount of organic matter in the soil. This outcome highlights the importance of including matrix-specific calibration in future studies considering a wide range of microplastic types, to avoid underestimation of microplastic contamination. We show here that methods for extracting microplastics from soils can be simple, cost-effective and widely applicable, which will enable the advancement of microplastic research in terrestrial environments.

Colorimetric loop-mediated isothermal amplification (LAMP) for cost-effective and quantitative detection of SARS-CoV-2: the change in color in LAMP-based assays quantitatively correlates with viral copy number.

Abstract: We demonstrate a loop-mediated isothermal amplification (LAMP) method to detect and amplify SARS-CoV-2 genetic sequences using a set of in-house designed initiators that target regions encoding the N protein. We were able to detect and amplify SARS-CoV-2 nucleic acids in the range of 62 to 2 × 105 DNA copies by this straightforward method. Using synthetic SARS-CoV-2 samples and RNA extracts from patients, we demonstrate that colorimetric LAMP is a quantitative method comparable in diagnostic performance to RT-qPCR (i.e., sensitivity of 92.85% and specificity of 81.25% in a set of 44 RNA extracts from patients analyzed in a hospital setting).

Detection of the SARS-CoV-2 spike protein in saliva with Shrinky-Dink© electrodes.

Abstract: Using the children's toy, Shrinky-Dink©, we present an aptamer-based electrochemical (E-AB) assay that recognizes the spike protein of SARS-CoV-2 in saliva for viral infection detection. The low-cost electrodes are implementable at population scale and demonstrate detection down to 1 ag mL-1 of the S1 subunit of the spike protein.

Recent advancements in the detection of organophosphate pesticides: a review.

Abstract: Organophosphorus pesticides (OPPs) are generally utilized for the protection of crops from pests. Because the use of OPPs in various agricultural operations has expanded dramatically, precise monitoring of their concentration levels has become the critical issue, which will help in the protection of ecological systems and food supply. However, the World Health Organization (WHO) has classified them as extremely dangerous chemical compounds. Taking their immense use and toxicity into consideration, the development of easy, rapid and highly sensitive techniques is necessary. Despite the fact that there are numerous conventional ways for detecting OPPs, the development of portable sensors is required to make routine analysis considerably more convenient. Some of these advanced techniques include colorimetric sensors, fluorescence sensors, molecular imprinted polymer-based sensors, and surface plasmon resonance-based sensors. This review article specifically focuses on the colorimetric, fluorescence and electrochemical sensors. In this article, the sensing strategies of these developed sensors, analytical conditions and their respective limit of detection are compiled.

Suspect and non-target screening: the last frontier in environmental analysis.

Abstract: Suspect and non-target screening (SNTS) techniques are arising as new analytical strategies useful to disentangle the environmental occurrence of the thousands of exogenous chemicals present in our ecosystems. The unbiased discovery of the wide number of substances present over environmental analysis needs to find a consensus with powerful technical and computational requirements, as well as with the time-consuming unequivocal identification of discovered analytes. Within these boundaries, the potential applications of SNTS include the studies of environmental pollution in aquatic, atmospheric, solid and biological samples, the assessment of new compounds, transformation products and metabolites, contaminant prioritization, bioremediation or soil/water treatment evaluation, and retrospective data analysis, among many others. In this review, we evaluate the state of the art of SNTS techniques going over the normalized workflow from sampling and sample treatment to instrumental analysis, data processing and a brief review of the more recent applications of SNTS in environmental occurrence and exposure to xenobiotics. The main issues related to harmonization and knowledge gaps are critically evaluated and the challenges of their implementation are assessed in order to ensure a proper use of these promising techniques in the near future.

Advances in epitope molecularly imprinted polymers for protein detection: a review.

Abstract: Epitope molecularly imprinted polymers (EMIPs) are novel imprinted materials using short characteristic peptides as templates rather than entire proteins. To be specific, the amino acid sequence of the template peptide is the same as an exposed N- or C-terminus of a target protein, or its amino acid composition and sequence replicate a similar conformational arrangement as the same amino acid residues on the surface of the target protein. EMIPs have a good application prospect in protein research. Herein, we focus on classification of epitope imprinting techniques, methods of epitope immobilization on matrix materials including boronate affinity immobilization, covalent bonding immobilization, physical adsorption immobilization and metal ion chelation immobilization, and application of EMIPs in peptides, proteins, target imaging and target therapy fields. Finally, the main problems and future development are summarized.

An electrochemical sensor based on hierarchical nickel oxide nanostructures doped with indium ions for voltammetric simultaneous determination of sunset yellow and tartrazine colorants in soft drink powders

Abstract: The current study was designed to develop a single-step and simple approach to effectively fabricate three-dimensional raspberry-like In3+/NiO hierarchical nanostructures (In3+/NiO RLHNSs) as a modifier, which was subsequently characterized by the techniques of X-ray diffraction (XRD), energy dispersive spectrometry (EDS) and field emission scanning electron microscopy (FE-SEM). The new prepared nano-modifier was practically used to co-detect electrochemically sunset yellow and tartrazine dyes. Potent sensitivity and acceptable selectivity were obtained for the produced In3+/NiO RLHNSs to co-detect both the food colorants, thus providing oxidation peaks in differential pulse voltammetry (DPV) with a peak potential separation of ca. 190 mV. The results showed a 5.14-fold and 8.07-fold increase in the electrochemical response of our modified electrode to sunset yellow and tartrazine, respectively, compared to the control (the unmodified electrode). Limits of detection of 2.7 and 3.1 nM were calculated for sunset yellow and tartrazine, respectively. The results from the interaction of common food additives showed satisfactory outcomes for the application of this method in determining sunset yellow and tartrazine in several beverage specimens. Other useful documentation was obtained for the production of portable food additive sensors.

Chiral porous organic frameworks and their application in enantioseparation

Abstract: Porous organic frameworks (POFs) are a kind of porous material with a network structure composed of repeated monomers, which have excellent physical and chemical properties, such as a high surface area, high porosity, uniform pore sizes and structural diversity, and which have aroused broad interest among researchers. With the rapid development of materials science, increasingly more porous materials have been developed and applied, especially metal organic frameworks (MOFs) and covalent organic frameworks (COFs), which have been widely applied in the fields of luminous materials, catalytic research, adsorption and drug transport. One of the most important applications for chiral porous materials is in chiral separation and these materials have become a research hotspot in the field of chromatographic separation and analysis in recent years. In this review, from the viewpoint of enantioseparation, the synthesis of chiral porous materials and their applications in high-performance liquid chromatography (HPLC), capillary electrochromatography (CEC), and gas chromatography (GC) are reviewed. The typical applications of MOFs in solid-phase microextraction (SPME) are also discussed.

Detection of RNA viruses from influenza and HIV to Ebola and SARS-CoV-2: a review.

Abstract: RNA-based viruses likely make up the highest pandemic threat among all known pathogens in about the last 100 years, since the Spanish Flu of 1918 with 50 M deaths up to COVID-19. Nowadays, an efficient and affordable testing strategy for such viruses have become the paramount target for the fields of virology and bioanalytical chemistry. The detection of the viruses (influenza, hepatitis, HIV, Zika, SARS, Ebola, SARS-CoV-2, etc.) and human antibodies to these viruses is described and tabulated in terms of the reported methods of detection, time to results, accuracy and specificity, if they are reported. The review is focused, but not limited to publications in the last decade. Finally, the limits of detection for each representative publication are tabulated by detection methods and discussed. These methods include PCR, lateral flow immunoassays, LAMP-based methods, ELISA, electrochemical methods (e.g., amperometry, voltammetry), fluorescence spectroscopy, AFM, SPR and SERS spectroscopy, silver staining and CRISPR-Cas based methods, bio-barcode detection, and resonance light scattering. The review is likely to be interesting for various scientists, and particularly helpful with information for establishing interdisciplinary research.

Development and validation of a RP-UPLC method for the determination of betamethasone dipropionate impurities in topical formulations using a multivariate central composite design.

Abstract: The current study presents a specific, accurate, simple, and rapid UPLC method for the determination of impurities present in cream and ointment formulations of betamethasone dipropionate (BMD). The analytical method was optimized using central composite design (CCD) prior to the method validation. Critical Process Parameters (CPPs) and Critical Quality Attributes (CQAs) were identified for the analytical method. A total of 17 experiments were carried out and verified the individual and interaction effects of CPPs. The CPPs were optimized using a numerical method by keeping the CQAs within the desired range (R1–R2: minimize & R3–R5: maximize) as an optimization goal. Optimized chromatographic separation was achieved using a Waters Acquity UPLC BEH C18, 100 mm × 2.1 mm, 1.7 μm column with a gradient mode of elution comprising 20 mM phosphate buffer: ACN 70 : 30, v/v as mobile phase-A and 20 mM phosphate buffer: ACN 30 : 70, v/v as mobile phase-B. The developed method was validated in accordance with ICH guidelines. The validation data conclude that the developed method is specific, accurate, linear, precise, rugged, and robust for the quantification of impurities in BMD topical formulations.

Analytical applications of single particle inductively coupled plasma mass spectrometry: a comprehensive and critical review.

Abstract: Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) refers to the use of ICP-MS as a particle counting technique. When ICP-MS measurements are performed at very high data acquisition frequencies, information about (nano)particles containing specific elements and their dissolved forms can be obtained (element mass per particle, size and number and mass concentrations). As a result of its outstanding performance, SP-ICP-MS has become a relevant technique for the analysis of complex samples containing inorganic nanoparticles. This review discusses the maturity level achieved by the technique through the methods developed for the detection, characterisation and quantification of engineered and natural (nano)particles. The application of these methods in different analytical scenarios is comprehensively reviewed and critically discussed, with special attention to their current technical and metrological limitations. The emergent applications of SP-ICP-MS in the field of nanoparticle-tagged immunoassay and hybridization methods are also reviewed.

Facile synthesis of biomass waste-derived fluorescent N, S, P co-doped carbon dots for detection of Fe3+ ions in solutions and living cells.

Abstract: Fluorescent carbon dots derived from natural biomass have received widespread attention in recent years due to their superior optical and chemical properties. In this work, we proposed a method to synthesize fluorescent nitrogen, sulfur, and phosphorus co-doped carbon dots (NSP-CDs) using biomass waste as a precursor. The blue emitting carbon dots were prepared from the seeds of green pepper, and Fe3+ ions could quench the fluorescence of NSP-CDs. Therefore, a fluorescent "turn-off" sensor based on NSP-CDs was constructed for the detection of Fe3+ ions. Further, NSP-CDs were evaluated as a fluorescent biosensor for the detection of Fe3+ in tap water and lake water samples, showing their potential value in practical applications. The cytotoxicity test further confirmed that NSP-CDs have good biocompatibility and can be extended to cell imaging and intracellular Fe3+ detection. The proposed method is simple, economical and green, which can meet the requirements of environmental monitoring and biological imaging.

Recent advances in selective formaldehyde detection in biological and environmental samples by fluorometric and colorimetric chemodosimeters.

Abstract: Formaldehyde, a highly reactive carbonyl species, has been widely used in day-to-day life owing to its numerous applications in essential commodities, etc.; the extrusion of formaldehyde from these sources basically leads to increased formaldehyde levels in the environment. Additionally, formaldehyde is endogenously produced in the human body via several biological processes. Considering the adverse effects of formaldehyde, it is highly important to develop an efficient and reliable method for monitoring formaldehyde in environmental and biological samples. Several chemodosimeters (reaction-based sensing probes) have been designed and synthesized to selectively detect the presence of formaldehyde utilizing the photophysical properties of molecules. In this review, we have comprehensively discussed the recent advances in the design principles and sensing mechanisms of developed probes and their biological/environmental applications in selective formaldehyde detection and imaging endogenous formaldehyde in cells. We have summarized the literature based on three different categories: (i) the Schiff base reaction, (ii) the 2-aza-Cope sigmatropic rearrangement reaction and (iii) miscellaneous approaches. In all cases, reactions are accompanied by changes in color and/or emission that can be detected by the naked eye.

New and sensitive HPLC-UV method for concomitant quantification of a combination of antifilariasis drugs in rat plasma and organs after simultaneous oral administration.

Abstract: A combination treatment comprising ivermectin (IVM), albendazole (ABZ) and doxycycline (DOX) is often prescribed for lymphatic filariasis patients. Nevertheless, there has not been an analytical method established and documented to determine these compounds simultaneously. Herein, we report a new high-performance liquid chromatographic method coupled with a UV detector (HPLC-UV) to quantify these drugs in plasma and organs. This developed analytical method was validated according to the International Conference on Harmonization (ICH) and US Food and Drug Administration (FDA) guidelines. The validated method was successfully employed to analyze IVM, ABZ along with its metabolites (albendazole sulfoxide (ABZ-OX) and albendazole sulfone (ABZ-ON)), and DOX in the plasma and organs of Wistar rats after simultaneous oral administration. An Xselect CSH™ C18 HPLC column was utilized as a stationary phase, with a mobile phase consisting of 0.1% v/v trifluoracetic acid in water and acetonitrile with a run time of 20 min. The calibration curves in biological samples were found to be linear across the concentration range of 0.01-5 μg mL-1 for IVM, ABZ and ABZ metabolites, and 0.025-10 μg mL-1 for DOX with an R value ≥0.998 in each case. The validated method was found to be selective, precise and accurate. Finally, the method developed in this study was deployed to assess the pharmacokinetic profiles and biodistribution of the combination of drugs after oral administration to Wistar rats. The validated HPLC-UV method in this study provides an extensive range of prospective applications for pharmacokinetic-based studies, therapeutic drug monitoring and toxicology.

Application of magnetic carbon nano-onions in dispersive solid-phase extraction combined with DLLME for extraction of pesticide residues from water and vegetable samples

Abstract: A dispersive solid-phase microextraction method based on magnetic carbon nano-onions (MCNOs) was developed for the extraction and preconcentration of some pesticides from water and vegetable samples. For more cleanup and preconcentration, a dispersive liquid-liquid microextraction (DLLME) method was employed after performing the first step. In this method, firstly, MCNOs were prepared and then used for adsorption of the analytes from the sample solution. After that, the adsorbed analytes were eluted with an appropriate water-miscible organic solvent and used as a dispersive solvent in the following DLLME procedure. The extracted analytes were quantified by gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring (SIM) mode. Various factors affecting the method efficiency such as sorbent weight, salt effect, pH, temperature, and type and volume of eluent and extraction solvent were optimized. This method showed wide linear ranges with a coefficient of determination ≥ 0.994, and low limits of detection (0.001-0.005 ng mL-1) and quantification (0.003-0.019 ng mL-1) under optimal conditions. Also, a good precision (relative standard deviation ≤ 8.6%) for five replicates and a satisfactory accuracy (mean relative recoveries between 82 and 99%) were obtained. It can be considered as an efficient and environment friendly method for the extraction of analytes from vegetable and fruit juices and water samples.

Green and sensitive spectrofluorimetric determination of Remdesivir, an FDA approved SARS-CoV-2 candidate antiviral; application in pharmaceutical dosage forms and spiked human plasma.

Abstract: Fluorescence spectroscopy has gained much attention over the last few years. Its advantages cover both analytical performance as well as ecological greenness. The quality control of pharmaceuticals requires sensitive, fast and economic methodologies to provide a high throughput at desirable costs. The low energy and decreased solvent consumption make this technique green as well as economic, and hence it is much preferred by pharmaceutical industries. Remdesivir is a recent antiviral, previously used for the treatment of Ebola virus infections, which was approved by the US-FDA in 2020 for treatment of infections caused by SARS-CoV-2 virus. Formulation and wide-scale production of this drug started recently and hence methodologies related to its quality control are highly required. A smart spectrofluorimetric method was validated as per the US-FDA guidelines for the facile estimation of Remdesivir. The assay of Remdesivir was based on its native fluorescence measurements at pH 4 and wavelengths of 244/405 nm. Calibration was achieved over the range of 1.0-65.0 ng mL-1. Different variables affecting the proposed methodology were studied to achieve maximum sensitivity, at limits of detection and quantification of 0.287 and 0.871 ng mL-1, respectively. The developed method is regarded as the first spectrofluorimetric one for the estimation of Remdesivir. The developed method was also utilized for the determination of the drug in its formulated IV infusion and in spiked human plasma. Statistical analysis verified that this method is accurate and reproducible. Moreover, the ecological impact of the developed procedures was evaluated on two recently reported assessment metrics, the Green Analytical Procedure Index (GAPI) and AGREE-analytical greenness metric, to emphasize the greenness of the procedure.

Flexible paper-based label-free electrochemical biosensor for the monitoring of miRNA-21 using core-shell Ag@Au/GQD nano-ink: a new platform for the accurate and rapid analysis by low cost lab-on-paper technology.

Abstract: miRNA-21 is one of the most famous and prominent microRNAs that is important in the development and emergence of cancers So, the sensitive and selective monitoring of miRNA-21 as a very common biomarker in cancer treatment is necessary In this work, a novel paper-based electrochemical peptide nucleic acid (PNA) sensor was developed for the detection of miRNA-21 in human plasma samples by using Ag@Au core-shell nanoparticles electrodeposited on graphene quantum dots (GQD) conductive nano-ink (Ag@Au core-shell/GQD nano-ink), which was designed directly by writing pen-on paper technology on the surface of photographic paper This nano-ink has a great surface area for biomarker immobilization The prepared paper-based biosensor is very small and cheap, and also has high stability and sensitivity Hybridization of PNA was measured using various electrochemical techniques, such as cyclic voltammetry (CV), square wave voltammetry (SWV) and chronoamperometry (ChA) FE-SEM (Field Scanning Electron Microscope), TEM (Transmission Electron Microscope), EDS and DLS (Dynamic Light Scattering) tests were performed to identify the engineering safety sensor Under optimal conditions, the linear range for the calibration curve was from 5 pM to 5 μM, and the achieved LLOQ was 5 pM The obtained results recommended that the proposed bioassay might be suitable for an early diagnosis of cancer based on the inhibition of the expression of miRNA-21, which activates the enzyme caspase and accelerates apoptotic proteins and death in tumor cells

Aptamer-based biosensors and their implications in COVID-19 diagnosis.

Abstract: Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), a novel infectious member of the coronavirus family, has caused millions of cases of infection and deaths all over the world, and been declared a pandemic by the World Health Organization. Conventional laboratory-based diagnostic testing has faced extreme difficulties in meeting the overwhelming demand for testing worldwide, and this has brought about a pressing need for cost-effective rapid diagnosis. There has been a surge in the number of prototypes of diagnostic kits developed, although many of these have been found to be lacking in terms of their accuracy and sensitivity. One type of chip-based diagnostic platform is the aptamer-based biosensor. Aptamers are artificially synthesized oligonucleotides that are capable of specifically binding to a target antigen. As of now, some aptamers have been reported for SARS-CoV-2. Although many ultrasensitive aptasensors have been developed for viruses, few have been successfully adapted for SARS-CoV-2 detection. Our review discusses the recent developments in the domain of SARS-CoV-2 specific aptamer isolation, the design of electrochemical and optical aptasensors, and the implications of aptasensor-based COVID-19 diagnosis.

Self-replicating catalyzed hairpin assembly for rapid aflatoxin B1 detection.

Abstract: Herein, a rapid signal amplified aflatoxin B1 (AFB1) detection system based on self-replicating catalyzed hairpin assembly (SRCHA) has been constructed. In this SRCHA system, trigger DNA was initially blocked and two split trigger DNA sequences were integrated into two hairpin auxiliary probes, H1 and H2, respectively. In the presence of AFB1, the aptamer sequence was recognized by AFB1 and trigger DNA was released, which can initiate a CHA reaction and lead to the formation of a helix DNA H1–H2 complex. Then this complex can dissociate double-stranded probe DNA (F–Q) and the fluorescence signal was recovered. Meanwhile, the two split trigger DNA sequences came into close-enough proximity and a trigger DNA replica was formed. Then the obtained replicas can trigger an additional CHA reaction, leading to the rapid and significant enhancement of the fluorescence signal, and AFB1 can be detected within 15 min with a detection limit of 0.13 ng mL−1. This AFB1 detection system exhibits potential application in the on-site rapid detection of AFB1.

2D bimetallic Ni/Fe MOF nanosheet composites as a peroxidase-like nanozyme for colorimetric assay of multiple targets.

Abstract: In this contribution, 2D Ni/Fe MOF nanosheets were synthesized by a simple two-step ultrasound strategy at room temperature, i.e. the 2D Ni-MOF with a lamellar structure was first synthesized by the top-down ultrasonic assisted stripping route, followed by introducing Fe3+ ions as a metal node and terephthalic acid as an organic ligand to form 2D Ni/Fe MOF nanosheets that exhibited weak oxidase-like and strong peroxidase-like properties. Relative to that of the single metal Ni-MOF and Fe-MOF, the peroxidase-mimicking capability of the 2D Ni/Fe MOF nanosheets increased by over 14-fold and 3-fold, respectively. Reactive oxygen trials indicated that the 2D Ni/Fe MOF nanosheets can efficiently catalyze the decomposition of H2O2 to generate the ˙OH and O2˙− radicals, which can oxidize TMB to oxTMB from colorless to blue. The kinetic trial demonstrated the high affinity of the 2D Ni/Fe MOF nanosheet to H2O2 with a Km of 0.037 mM, which was 100 times lower than that of HRP. These impressive characteristics are likely related to the good dispersion of the in situ formed Fe MOF in the 2D Ni-MOF nanosheet structure with coordinatively unsaturated metal sites. This allows the 2D Ni/Fe MOF nanosheets to expose more active metal sites and to enhance the intrinsic catalytic activity of each site due to the synergistic interaction between the two metals. Interestingly, glutathione can obviously restrict the peroxidase-like activity of the 2D Ni/Fe MOF nanosheet, while the inhibited TMB oxidation can be restored upon further introducing Hg2+ ions due to the high and specific affinity of Hg2+ to thiol groups in glutathione. Based on the above facts, the 2D Ni/Fe MOF nanozyme was used to construct a nanoplatform to determine multiple targets, i.e. H2O2, glutathione and Hg2+. The 2D Ni/Fe MOF nanozyme-based colorimetric assay exhibits a linear response to H2O2, glutathione and Hg2+ ions over the 0.01–100 μM, 0.02–100 μM, and 100 nM to 200 μM ranges, respectively. The limits of detection (3σ) for the determination of H2O2, glutathione and Hg2+ are 10 nM, 10 nM, and 100 nM, respectively. This method was used to determinate the content of Hg2+ ions in real water samples.

A double-potential ratiometric electrochemiluminescence platform based on g-C3N4 nanosheets (g-C3N4 NSs) and graphene quantum dots for Cu2+ detection.

Abstract: A new kind of convenient, low-cost double-potential ratiometric ECL sensing platform for the quantification of Cu2+ was developed with carbon nitride nanosheets (g-C3N4 NSs) and graphene quantum dots (GQDs) as ECL luminophores. g-C3N4 NSs mixed with multi-walled carbon nanotubes (MWCNTs) was immobilized on a glass carbon electrode (GCE) and produced strong cathodic ECL at a potential of -1.2 V (vs. Ag/AgCl), while GQDs in the solution gave anodic ECL at +2.5 V. MWCNTs were used here to amplify the ECL signal of g-C3N4 NSs. The addition of Cu2+ causes the cathodic ECL signal from g-C3N4 to decline, while the anodic ECL signal from GQDs remains unchanged. With the anodic ECL signal as an internal reference, a double-potential ratiometric ECL sensing platform for Cu2+ was established. The ratio of the cathodic signal intensity to anodic signal intensity showed a linear response to the Cu2+ concentration over a range from 5.0 × 10-10 to 1.0 × 10-6 mol L-1 and the detection limit was 0.37 nmol L-1 (3σ/S). Such a construction strategy alleviates the interference from the environment and therefore improves the detection accuracy of Cu2+. Compared with other methods for Cu2+ detection, this method is simpler and more sensitive.

Development of an electrochemical sensor for the determination of antibiotic sulfamethazine in cow milk using graphene oxide decorated with Cu-Ag core-shell nanoparticles.

Abstract: Determination and sensing of antibiotics in dairy products are the biggest challenges in the world. In continuation of our earlier study, a facile and novel determination method for the detection of sulfamethazine (SMZ) in cow milk has been developed using a glassy carbon electrode modified with graphene oxide decorated with Cu–Ag core–shell nanoparticles. The Cu–Ag core–shell nanoparticles and graphene oxide were synthesized and characterized via different techniques such as TEM, SEM, XRD and FTIR. The as-synthesized Cu–Ag core–shell nanoparticles were used for the decoration of the glassy carbon electrode modified with graphene oxide. The electroanalytical measurements including cyclic voltammetry and square wave voltammetry were performed and compared with HPLC, which was utilized for the determination of SMZ in cow milk. The experimental conditions were optimized to obtain a well-defined response signal. The concentration linear range was 10–1000 μM and the limit of detection was 0.46 μM for S/N = 3. The obtained results show good agreement with HPLC reported data.

Smartphone-based colorimetric detection system for portable health tracking

Abstract: Colorimetric tests for at-home health monitoring became popular 50 years ago with the advent of the urinalysis test strips, due to their reduced costs, practicality, and ease of operation. However, developing digital systems that can interface these sensors in an efficient manner remains a challenge. Efforts have been put towards the development of portable optical readout systems, such as smartphones. However, their use in daily settings is still limited by their error-prone nature associated to optical noise from the ambient lighting, and their low sensitivity. Here, a smartphone application (Colourine) to readout colorimetric signals was developed on Android OS and tested on commercial urinalysis test strips for pH, proteins, and glucose detection. The novelty of this approach includes two features: a pre-calibration step where the user is asked to take a photo of the commercial reference chart, and a CIE-RGB-to-HSV color space transformation of the acquired data. These two elements allow the background noise given by environmental lighting to be minimized. The sensors were characterized in the ambient light range 100–400 lx, yielding a reliable output. Readouts were taken from urine strips in buffer solutions of pH (5.0–9.0 units), proteins (0–500 mg dL−1) and glucose (0–1000 mg dL−1), yielding a limit of detection (LOD) of 0.13 units (pH), 7.5 mg dL−1 (proteins) and 22 mg dL−1 (glucose), resulting in an average LOD decrease by about 2.8 fold compared to the visual method.

Dual-state emission difluoroboron derivatives for selective detection of picric acid and reversible acid/base fluorescence switching.

Abstract: A novel difluoroboron derivative (TPEBF) containing α-cyanostilbene and tetraphenylethylene units has been designed and synthesized. TPEBF emits strong fluorescence both in dilute solutions (ΦFL = 19.3% in THF) and in the solid state (ΦFL = 49.3%), which is significantly distinct from the case of the aggregation-caused quenching (ACQ) and aggregation-induced emission (AIE) chromophores. The dual-state emission properties of the compound overcome the limitation of single-state luminescence and enable it to be used in both solid and solution states. TPEBF with strong emission in solution is utilized for sensing picric acid (PA) with high selectivity and sensitivity in THF (LOD = 497 nM) and aqueous media (LOD = 355 nM). The mechanism was described for the synergy of fluorescence resonance energy transfer (FRET) and photoinduced energy transfer (PET) based on the UV-vis absorption and fluorescence spectra, 1H NMR and theoretical calculations results. On the other hand, the highly efficient emission in the solid state allows the compound to be cast on paper to switch external acid/base stimuli.

Combining prior knowledge with input selection algorithms for quantitative analysis using neural networks in laser induced breakdown spectroscopy.

Abstract: Laser-induced breakdown spectroscopy (LIBS) is an emerging technique for the analysis of rocks and mineral samples. Artificial neural networks (ANNs) have been used to estimate the concentration of minerals in samples from LIBS spectra. These spectra are very high dimensional data, and it is known that only specific wavelengths have information on the atomic and molecular features of the sample under investigation. This work presents a systematic methodology based on the Akaike information criterion (AIC) for selecting the wavelengths of LIBS spectra as well as the ANN model complexity, by combining prior knowledge and variable selection algorithms. Several variable selection algorithms are compared within the proposed methodology, namely KBest, a least absolute shrinkage and selection operator (LASSO) regularization, principal component analysis (PCA), and competitive adaptive reweighted sampling (CARS). As an illustrative example, the estimation of copper, iron and arsenic concentrations in pelletized mineral samples is performed. A dataset of LIBS emission spectra with 12 287 wavelengths in the range of 185–1049 nm obtained from 131 samples of copper concentrates is used for regression analysis. An ANN is then trained considering the selected reduced wavelength data. The results are satisfactory using LASSO and CARS algorithms along with prior knowledge, showing that the proposed methodology is very effective for selecting wavelengths and model complexity in quantitative analyses based on ANNs and LIBS.

A simple colorimetric method for viable bacteria detection based on cell counting Kit-8.

Abstract: In this study, Cell Counting Kit-8 (CCK-8) was introduced to detect the concentration of live bacteria for the first time depending on the redox reaction between CCK-8 solution and dehydrogenase. CCK-8 solution can be reduced to form water soluble orange-yellow formazan by the dehydrogenase present in bacterial cells, and the concentration of live bacteria is proportional to the absorbance value of formazan at 450 nm. Based on this principle, Staphylococcus aureus and Escherichia coli were chosen as the model bacteria. The optimal detection conditions were investigated and a good linear relationship was obtained in the concentration range from 2.600 × 102 to 1.160 × 109 CFU mL−1 with a linear equation of Y = 0.06305 log10 X-0.1153 (X in CFU mL−1, R2 = 0.9747) for S. aureus and 9.750 × 102 to 6.000 × 108 CFU mL−1 with a linear equation of Y = 0.06122 log10 X-0.1358 (X in CFU mL−1, R2 = 0.9958) for E. coli. The CCK-8 based viable bacteria detection method can be completed within 2 h with a wide bacterial detection concentration range. Satisfactory results were obtained when applied to an actual sample analysis and there is a good consistency between the proposed CCK-8 based method and the traditional plate counting method. More importantly, this method can realize the one-time detection of a large number of samples with high sensitivity, which suggests its great potential in high-throughput bacterial detection.

An electrochemical sensor based on an anti-fouling membrane for the determination of histamine in fish samples

Abstract: Electrochemical determination of histamine (HA) is quite challenging owing to the high oxidation potential and electrode fouling from HA oxide polyhistamine, which leads to poor sensitivity and unrepeatable measurement. In the present work, a simple, sensitive and repeatable electrochemical measurement of HA was developed based on a Nafion and multi-walled carbon nanotube (MWCNTs) composite membrane modified glassy carbon electrode (GCE). Compared with the bare GCE, the Nafion and MWCNT composite membrane modified electrode significantly enhanced the oxidation peak current and reduced the peak potential to 1.12 V (vs. SCE). Moreover, the characterization of the modified electrode by XPS and EIS showed that polyhistamine scarcely deposited on the composite membrane of the modified GCE, which made it possible to realize repeatable electrochemical measurement of HA. The electrochemical oxidation behavior of HA on the modified electrode was studied by differential pulse voltammetry (DPV). The oxidation peak current has linear and natural log-linear relationships with HA concentration in the range of 20-200 μmol L-1 and 0.5-10 μmol L-1, respectively. The detection limit was 0.39 μmol L-1 (S/N = 3). The modified electrode could be used to determine 100 μmol L-1 HA ten times repeatedly; the peak currents in consecutive runs were all above 95% of the initial response. This method was also successfully applied to the determination of HA in fish samples and recoveries ranged from 98.2 to 101.2%.

Disposable non-enzymatic electrochemical glucose sensors based on screen-printed graphite macroelectrodes modified via a facile methodology with Ni, Cu, and Ni/Cu hydroxides are shown to accurately determine glucose in real human serum blood samples.

Abstract: A three dimensional (3D) non-enzymatic glucose disposable electrochemical sensor based on screen-printed graphite macroelectrodes (SPEs), modified with nickel hydroxide (Ni(OH)2/SPE), copper hydroxide (Cu(OH)2/SPE) and mixed (Ni(OH)2/Cu(OH)2/SPE) microstructures were prepared by a facile and cost-effective electrochemical method for the first time. Their morphologies and structures were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The electrochemical performances of the modified SPEs were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometric measurements. EIS experiments showed lower charge transfer resistance Rct values for the modified SPEs, calculated to be 29.24 kΩ, 22.58 kΩ, 13.27 kΩ and 36.48 kΩ for Ni(OH)2/SPE, Cu(OH)2/SPE, Ni(OH)2/Cu(OH)2/SPE, and SPE, respectively. Under optimal experimental conditions, the results reveal that CV, amperometry and EIS can be readily applied to determine glucose using all of the fabricated sensors, however in terms of an accessible and clinically relevant linear range for the electroanalytical detection of glucose, CV is preferred, where Cu(OH)2/SPE exhibits the largest linear range from 1 μM to 20 mM (R2 = 0.997). In terms of sensitivity and the detection limit however, amperometry appeared to be a better choice of technique, particularly with Ni(OH)2/Cu(OH)2/SPE which demonstrated the highest sensitivity of 2029 μA mM−1 cm−2 and the lowest detection limit of 0.2 μM (S/N = 3). Excellent selectivity was evident against common interfering species, and it was shown to be possible to obtain satisfactory results in human blood serum samples using the as-fabricated sensors. The low cost of the SPEs, the facile preparation and observed clinically relevant analytical sensitivities and limit of detections towards the sensing of glucose make these screen-printed macroelectrode based electrochemical sensing platforms promising for routine human blood serum glucose analysis.