Showing papers in "Mikrochimica Acta in 2014"
TL;DR: This review first gives an introduction into the topic of screen-printed electrodes for biosensing and is subdivided into sections (a) on DNA sensors, (b) on aptasensors, (c) on immunosensor, (d) on enzymatic biosensors.
Abstract: Screen-printing is one of the most promising approaches towards simple, rapid and inexpensive production of biosensors. Disposable biosensors based on screen printed electrodes (SPEs) including microelectrodes and modified electrodes have led to new possibilities in the detection and quantitation of biomolecules, pesticides, antigens, DNA, microorganisms and enzymes. SPE-based sensors are in tune with the growing need for performing rapid and accurate in-situ analyses and for the development of portable devices. This review (with 226 refs.) first gives an introduction into the topic and then is subdivided into sections (a) on DNA sensors (including methods for the detection of hybridization and damage), (b) on aptasensors (for thrombin, OTA, immunoglobulins and cancer biomarkers), (c) on immunosensors (for microorganisms, immunoglobulins, toxins, hormones, lactoferrin and biomarkers), (d) on enzymatic biosensors (for glucose, hydrogen peroxide, various pharmaceuticals, neurotransmitters, amino acids, NADH, enzyme based sensors).
369 citations
TL;DR: Enzyme-free (also called nonenzymatic or direct) electrochemical sensors have been widely used for the determination of hydrogen peroxide, glucose, and uric acid as mentioned in this paper.
Abstract: Enzyme-free (also called non-enzymatic or direct) electrochemical sensors have been widely used for the determination of hydrogen peroxide, glucose, and uric acid. This review covers the recent progress made in this field. We also discuss the respective sensor materials which have strong effect on the electro-catalytic properties of the electrodes and govern the performance of these sensors. In addition, perspectives and current challenges of enzyme-free electrochemical sensors are outlined. Contains 142 references.
301 citations
TL;DR: The surface enhanced Raman spectroscopy (SERS) has emerged as one of the most promising analytical tools in recent years as mentioned in this paper. But its performance has not yet reached the state-of-the-art.
Abstract: Surface enhanced Raman spectroscopy (SERS) has emerged as one of the most promising analytical tools in recent years. Due to advantageous features such as sensitivity, specificity, ease of operation and rapidity, SERS is particularly well suited for environmental analysis. We summarize here some considerations with respect to the detection of pollutants by SERS and provide an overview on recent achievements in the determination of organic pollutants, heavy metal ions, and pathogens. Following an introduction into the topic and considering aspects of sensitivity, selectivity, reproducibility and portability, we are summarizing applications of SERS in the detection of pollutants, with sections on organic pollutants (pesticides, PAHs and PCBs, explosives), on heavy metal ions, and on pathogens. In addition, we discuss current challenges and give an outlook on applications of SERS in environmental analysis. Contains 174 references.
240 citations
TL;DR: In this paper, the authors summarized the recent work on the development of chemical sensors and biosensors based on the use of composites made from conducting polymers (CPs) and graphene.
Abstract: This review (with 79 references) summarizes the recent work on the development of chemical sensors and biosensors based on the use of composites made from conducting polymers (CPs) and graphene. Owing to the unique electrical, mechanical, optical, chemical and structural properties of CP and graphene, these kinds of composites have generated increasing interest in senor field. In this review, we first discuss methods for preparation of CP/GE composites by chemical, electrochemical, or physical methods including electrostatic interactions. We then cover aspects of the fabrication of modified electrodes and the performance of respective sensors with electrochemical, electronic or optical signal transduction. We then discuss sensors for the determination of inorganic and organic species, gases and vapors. We also review the state of the art in respective biosensors for hydrogen peroxide and glucose, for oligomers (DNA, RNA, and aptamers), for biogenic amines, NAD^+/NADH, cytochromes and the like, and in immunosensors. Finally, the perspective and current challenges of CP/GE composites for use in (bio)sensors are outlooked.
156 citations
TL;DR: Results show the development of an on-chip RPA (recombinase polymerase amplification) with simultaneous multiplex isothermal amplification and detection on a solid surface to be useful with respect to point-of-care testing and to enable simplified and miniaturized nucleic acid-based diagnostics.
Abstract: We report on the development of an on-chip RPA (recombinase polymerase amplification) with simultaneous multiplex isothermal amplification and detection on a solid surface. The isothermal RPA was applied to amplify specific target sequences from the pathogens Neisseria gonorrhoeae, Salmonella enterica and methicillin-resistant Staphylococcus aureus (MRSA) using genomic DNA. Additionally, a positive plasmid control was established as an internal control. The four targets were amplified simultaneously in a quadruplex reaction. The amplicon is labeled during on-chip RPA by reverse oligonucleotide primers coupled to a fluorophore. Both amplification and spatially resolved signal generation take place on immobilized forward primers bount to expoxy-silanized glass surfaces in a pump-driven hybridization chamber. The combination of microarray technology and sensitive isothermal nucleic acid amplification at 38 °C allows for a multiparameter analysis on a rather small area. The on-chip RPA was characterized in terms of reaction time, sensitivity and inhibitory conditions. A successful enzymatic reaction is completed in <20 min and results in detection limits of 10 colony-forming units for methicillin-resistant Staphylococcus aureus and Salmonella enterica and 100 colony-forming units for Neisseria gonorrhoeae. The results show this method to be useful with respect to point-of-care testing and to enable simplified and miniaturized nucleic acid-based diagnostics.
149 citations
TL;DR: An electrochemical glucose biosensor was developed by immobilizing glucose oxidase (GOx) on a glass carbon electrode that was modified with molybdenum disulfide (MoS2) nanosheets that were decorated with gold nanoparticles (AuNPs) as mentioned in this paper.
Abstract: An electrochemical glucose biosensor was developed by immobilizing glucose oxidase (GOx) on a glass carbon electrode that was modified with molybdenum disulfide (MoS2) nanosheets that were decorated with gold nanoparticles (AuNPs). The electrochemical performance of the modified electrode was investigated by cyclic voltammetry, and it is found that use of the AuNPs-decorated MoS2 nanocomposite accelerates the electron transfer from electrode to the immobilized enzyme. This enables the direct electrochemistry of GOx without any electron mediator. The synergistic effect the MoS2 nanosheets and the AuNPs result in excellent electrocatalytic activity. Glucose can be detected in the concentration range from 10 to 300 μM, and down to levels as low as 2.8 μM. The biosensor also displays good reproducibility and long-term stability, suggesting that it represents a promising tool for biological assays.
147 citations
TL;DR: In this article, the state of the art in methods for coating materials for use in solid phase microextraction (SPME) is discussed, with a focus on simple methods for deposition of different types of coatings.
Abstract: Introduced in the 1990s, solid-phase microextraction (SPME) has found numerous applications. This is due to the solventless nature of SPME and the large variety of sorbents and coatings available. Highly diverse procedures have been applied to coat supports such as fused silica fibers or metal wires with sorbents in order to enhance capability, selectivity and robustness of SPME. Lately, research also is directed towards more simple methods for deposition of different types of coatings. Several of these methods have resulted in better stability and higher effective surface areas of the coatings. This review (with 128 references) covers the state of the art in methods for coating materials for use in SPME. It is divided into the following sections: (a) Dip methods and physical agglutination methods, (b) sol-gel technology, (c) chemical grafting, (d) electrochemical methods for coating (such as electrodeposition, anodizing and electrophoretic deposition), (e) electrospinning, (f) liquidphase deposition, and (g) hydrothermal methods. A final section covers conclusions and future trends.
140 citations
TL;DR: A review of the progress made in enzymatic biosensors based on the use of metal oxide nanoparticles can be found in this article, where the authors discuss strategies for immobilization and functions of MONPs.
Abstract: Over the past decades, various techniques have been developed to obtain materials at a nanoscale level to design biosensors with high sensitivity, selectivity and efficiency. Metal oxide nanoparticles (MONPs) are of particular interests and have received much attention because of their unique physical, chemical and catalytic properties. This review summarizes the progress made in enzymatic biosensors based on the use of MONPs. Synthetic methods, strategies for immobilization, and the functions of MONPs in enzymatic biosensing systems are reviewed and discussed. The article is subdivided into sections on enzymatic biosensors based on (a) zinc oxide nanoparticles, (b) titanium oxide nanoparticles, (c) iron oxide nanoparticles, and (d) other metal oxide nanoparticles. While substantial advances have been made in MONPs-based enzymatic biosensors, their applications to real samples still lie ahead because issues such as reproducibility and sensor stability have to be solved. The article contains 256 references.
115 citations
TL;DR: This review covers three aspects of PCR-based microfluidic chip assays: sample preparation, target amplification, and product detection, and the challenges related to the miniaturization and integration of each assay are discussed.
Abstract: This review covers three aspects of PCR-based microfluidic chip assays: sample preparation, target amplification, and product detection. We also discuss the challenges related to the miniaturization and integration of each assay and make a comparison between conventional and microfluidic schemes. In order to accomplish these essential assays without human intervention between individual steps, the micro-components for fluid manipulation become critical. We therefore summarize and discuss components such as microvalves (for fluid regulation), pumps (for fluid driving) and mixers (for blending fluids). By combining the above assays and microcomponents, DNA testing of multi-step bio-reactions in microfluidic chips may be achieved with minimal external control. The combination of assay schemes with the use of micro-components also leads to rapid methods for DNA testing via multi-step bioreactions. Contains 259 references.
104 citations
TL;DR: In this paper, an aptasensor for the detection of Staphylococcus aureus by electrochemical impedance spectroscopy (EIS) was described, where single-stranded DNA was linked to a nanocomposite prepared from reduced graphene oxide (rGO) and gold nanoparticles (AuNP).
Abstract: We describe here an aptasensor for the ultrasensitive detection of Staphylococcus aureus by electrochemical impedance spectroscopy (EIS). Single-stranded DNA was linked to a nanocomposite prepared from reduced graphene oxide (rGO) and gold nanoparticles (AuNP). Thiolated ssDNA was covalently linked to the AuNPs linked to rGO, and probe DNA was immobilized on the surface of an AuNP-modified glassy carbon electrode to capture and concentrate Staph. aureus. The probe DNA of the aptasensor selectively captures the target bacteria in its three-dimensional space, and these results in a dramatic increase in impedance. Scanning electron microscopy, cyclic voltammetry and EIS were used to monitor the single steps of the electrode assembly process. The effect was utilized to quantify the bacteria in the concentration range from 10 to 106 cfu mL−1 and with a detection limit of 10 cfu mL−1 (S/N = 3). The relative standard deviation of Staphylococcus aureus detection was equal to 4.3 % (105 cfu mL−1, n = 7). In addition to its sensitivity, the biosensor exhibits high selectivity over other pathogens.
103 citations
TL;DR: In this article, an aptamer with high affinity against Salmonella typhimurium (S. typhimurus) was selected from an enriched oligonucleotide pool by a whole-cell SELEX process.
Abstract: We report on an aptamer with high affinity against Salmonella typhimurium (S. typhimurium) and selected from an enriched oligonucleotide pool by a whole-cell SELEX process in a method for the fluorimetric determination of S. typhimurium using a graphene oxide platform. In the absence of target, the fluorescence was fairly weak as result of the FAM-labeled aptamer adjacent to graphene oxide. If, however, the fluorophore is released from the graphene oxide due to the formation of the target/aptamer complexes, fluorescence intensity is substantially increased. Under the optimum conditions, the assay displays a linear response to bacteria in the concentration range from 1 × 103 to 1 × 108 CFU·mL−1, with a detection limit of 100 CFU·mL−1. The method is selective in that fluorescence is not much enhanced in case of other bacteria. This aptasensor displays higher sensitivity and selectivity than others and is believed to possess a large potential with respect to the rapid detection of bacteria.
TL;DR: In this paper, a fast method for sensitive extraction and determination of the metal ions silver(I), gold(III), copper(II), and palladium(II) was developed.
Abstract: We have developed a fast method for sensitive extraction and determination of the metal ions silver(I), gold(III), copper(II) and palladium(II). Fe3O4 magnetic nanoparticles were modified with polythiophene and used for extraction the metal ions without a chelating agent. Following extraction, the ions were determined by flow injection inductively coupled plasma optical emission spectrometry. The influence of sample pH, type and volume of eluent, amount of adsorbent, sample volume and time of adsorption and desorption were optimized. Under the optimum conditions, the calibration plots are linear in the 0.75 to 100 μg L−1 concentration range (R2 > 0.998), limits of detection in the range from 0.2 to 2.0 μg L−1, and enhancement factors in the range from 70 to 129. Precisions, expressed as relative standard deviations, are lower than 4.2 %. The applicability of the method was demonstrated by the successful analysis of tap water, mineral water, and river water.
TL;DR: This review covers the basic mechanisms of up-conversion luminescence, the methods for the synthesis and surface modification of biocompatible UCNPs, and aspects of the in vivo delivery ofUCNPs.
Abstract: Upconversion nanoparticles (UCNPs) represent a new class of fluorophores Both the excitation and (anti-Stokes) emission wavelengths are in the long wave part of the spectrum so that their luminescence can deeply penetrate tissues and cause low photodamage in biological samples Their large anti-Stokes shifts, sharp emission bands, zero auto-fluorescence from biological samples and high photostability renders them an ideal kind of fluorescent labels for a variety of analytical formats, for bioimaging in cancer therapy This review covers the basic mechanisms of up-conversion luminescence, the methods for the synthesis and surface modification of biocompatible UCNPs, and aspects of the in vivo delivery of UCNPs More specifically, we discuss (a) recent progress regarding UCNPs for multimodal targeted tumor imaging, (b) UCNP-based methods of biological detection and sensing, (c) the use of UCNPs in drug delivery, (d) applications in photodynamic therapy, photothermal therapy and radiotherapy Finally, we are addressing challenges and opportunities of this quickly emerging field Contains 362 references
TL;DR: The use of quercetin as novel reagent for preparation and functionalization of gold nanoparticles to colorimetric sensing of three aminoacids (arginine, histidine and lysine) is reported, providing a useful tool for the rapid visual and instrumental determination of the three amino acids.
Abstract: We report on the use of quercetin-functionalized gold nanoparticles (QC-AuNPs) as a colorimetric probe for the amino acids arginine (Arg), histidine (His) and lysine (Lys). The method is based on the aggregation of the QC-AuNPs that is caused by these amino acids and leads to a visually detectable color change from red to blue. The absorption maxima shift from 525 nm to 702, 693, and 745 nm, respectively. Aggregations are confirmed by dynamic light scattering (DLS) and transmission electron microscopic techniques (TEM). The effects of the QC concentration, temperature and reaction time for the preparation of QC-Au NPs were tested. Other amino acids do not interfere. Under the optimal conditions, linear relationships exist between the absorption ratios at 702/525 nm (for Arg), 693/525 nm (for His), and 745/525 nm (for Lys) over the concentrations ranges from 2.5–1,250 μM (Arg) and 1–1,000 μM (His and Lys), respectively. The respective limits of detection are 0.04, 0.03, and 0.02 μM. The method provides a useful tool for the rapid visual and instrumental determination of the three amino acids.
TL;DR: The SELEX method excels by its features of in vitro, high throughput and ease of operation.
Abstract: The method referred to as “systemic evolution of ligands by exponential enrichment” (SELEX) was introduced in 1990 and ever since has become an important tool for the identification and screening of aptamers. Such nucleic acids can recognize and bind to their corresponding targets (analytes) with high selectivity and affinity, and aptamers therefore have become attractive alternatives to traditional antibodies not the least because they are much more stable. Meanwhile, they have found numerous applications in different fields including food quality and safety monitoring. This review first gives an introduction into the selection process and to the evolution of SELEX, then covers applications of aptamers in the surveillance of food safety (with subsections on absorptiometric, electrochemical, fluorescent and other methods), and then gives conclusions and perspectives. The SELEX method excels by its features of in vitro, high throughput and ease of operation. This review contains 86 references.
TL;DR: In this paper, a carbon paste electrode (CPE) was modified with multiwalled carbon nanotubes (MWCNT) and an ionic liquid (IL), which gave three sharp and well separated oxidation peaks for ascorbic acid, dopamine (DA), and uric acid (UA).
Abstract: We describe the modification of a carbon paste electrode (CPE) with multiwalled carbon nanotubes (MWCNT) and an ionic liquid (IL). Electrochemical studies revealed an optimized composition of 60 % graphite, 20 % paraffin, 10 % MWCNT and 10 % IL. In a next step, the optimized CPE was modified with palladium nanoparticles (Pd-NPs) by applying a double-pulse electrochemical technique. The resulting electrode was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy. It gives three sharp and well separated oxidation peaks for ascorbic acid (AA), dopamine (DA), and uric acid (UA), with peak separations of 180 and 200 mV for AA-DA and DA-UA, respectively. The sensor enables simultaneous determination of AA, DA and UA with linear responses from 0.6 to 112, 0.1 to 151, and 0.5 to 225 μM, respectively, and with 200, 30 and 150 nM detection limits (at an S/N of 3). The method was successfully applied to the determination of AA, DA, and UA in spiked samples of human serum and urine.
TL;DR: The successful combination of fluorescent nanoparticle-based pathogen detection by LFIAs with a smart phone-based detection platform has resulted in a portable device with improved diagnosis features and having potential application in diagnostics and environmental monitoring.
Abstract: We are describing immunochromatographic test strips with smart phone-based fluorescence readout. They are intended for use in the detection of the foodborne bacterial pathogens Salmonella spp. and Escherichia coli O157. Silica nanoparticles (SiNPs) were doped with FITC and Ru(bpy), conjugated to the respective antibodies, and then used in a conventional lateral flow immunoassay (LFIA). Fluorescence was recorded by inserting the nitrocellulose strip into a smart phone-based fluorimeter consisting of a light weight (40 g) optical module containing an LED light source, a fluorescence filter set and a lens attached to the integrated camera of the cell phone in order to acquire high-resolution fluorescence images. The images were analysed by exploiting the quick image processing application of the cell phone and enable the detection of pathogens within few minutes. This LFIA is capable of detecting pathogens in concentrations as low as 105 cfu mL−1 directly from test samples without pre-enrichment. The detection is one order of magnitude better compared to gold nanoparticle-based LFIAs under similar condition. The successful combination of fluorescent nanoparticle-based pathogen detection by LFIAs with a smart phone-based detection platform has resulted in a portable device with improved diagnosis features and having potential application in diagnostics and environmental monitoring.
TL;DR: A comprehensive review of liquid phase microextraction (LPME) methods for the preconcentration and determination of pesticides in various matrices can be found in this paper, where sample treatment techniques in general, single-drop micro-extraction, extraction based on the use of ionic liquids, (d) solidified floating organic drop micro extraction, and various other techniques are discussed.
Abstract: Liquid phase microextraction (LPME) enables analytes to be extracted with a few microliters of an organic solvent. LPME is a technique for sample preparation that is extremely simple, affordable and virtually a solvent-free. It can provide a high degree of selectivity and enrichment by eliminating carry-over between single runs. A variety of solvents are known for the extraction of the various analytes. These features have led to the development of techniques such as single drop microextraction, hollow fiber LPME, dispersive liquid-liquid microextraction, and others. LPME techniques have been applied to the analysis of pharmaceuticals, food, beverages, and pesticides. This review covers the history of LPME methods, and then gives a comprehensive collection of their application to the preconcentration and determination of pesticides in various matrices. Specific sections cover (a) sample treatment techniques in general, (b) single-drop microextraction, (c) extraction based on the use of ionic liquids, (d) solidified floating organic drop microextraction, and various other techniques. Contains 149 references.
TL;DR: In this article, a simple method for the direct and quantitative determination of L-tryptophan (Trp) and L-tyrosine (Tyr) using a glassy carbon electrode (GCE) modified with single-walled carbon nanohorns (SWCNHs) was reported.
Abstract: We report a simple method for the direct and quantitative determination of L-tryptophan (Trp) and L-tyrosine (Tyr) using a glassy carbon electrode (GCE) modified with single-walled carbon nanohorns (SWCNHs). The SWCNH modified GCE exhibits high electrocatalytic activity towards the oxidation of both Trp and Tyr. It shows a linear response to Trp between 0.5 and 50 μM and to Tyr between 2 and 30 μM. The detection limits for Trp and Tyr are 50 nM and 400 nM, respectively. In addition, the modified GCE displays good selectivity and good sensitivity, thus making it suitable for the determination of Trp and Tyr in spiked serum samples.
TL;DR: In this paper, a novel type of porous metal-organic framework (MOF) was obtained from thiol-modified silica nanoparticles and the copper(II) complex of trimesic acid.
Abstract: A novel type of porous metal-organic framework (MOF) was obtained from thiol-modified silica nanoparticles and the copper(II) complex of trimesic acid. It is shown that this nanocomposite is well suitable for the preconcentration of Hg(II) ions. The nanocomposite was characterized by Fourier transfer infrared spectroscopy, X-ray powder diffraction, energy-dispersive X-ray diffraction and scanning electron microscopy. The effects of pH value, sorption time, elution time, the volume and concentration of eluent were investigated. Equilibrium isotherms were studied, and four models were applied to analyze the equilibrium adsorption data. The results revealed that the adsorption process obeyed the Langmuir model. The maximum monolayer capacity and the Langmuir constant are 210 mg g−1 and 0.273 L mg−1, respectively. The new MOF-based nanocomposite is shown to be an efficient and selective sorbent for Hg(II). Under the optimal conditions, the limit of detection is 20 pg mL−1 of Hg(II), and the relative standard deviation is <7.2 % (for n = 3). The sorbent was successfully applied to the rapid extraction of Hg(II) ions from fish, sediment, and water samples.
TL;DR: In this paper, a boron-doped diamond (BDD) electrode was modified with a nanocomposite prepared from carbon spheres (CSs; with an average diameter of 500nm) that were synthesized from resorcinol and formaldehyde, and then were coated with gold nanoparticles (AuNPs) by chemically growing them of the CSs.
Abstract: We report on a biosensor for organophosphate pesticides (OPs) by exploiting their inhibitory effect on the activity of acetylcholinesterase (AChE). A boron-doped diamond (BDD) electrode was modified with a nanocomposite prepared from carbon spheres (CSs; with an average diameter of 500 nm) that were synthesized from resorcinol and formaldehyde, and then were coated with gold nanoparticles (AuNPs) by chemically growing them of the CSs. Compared to a bare BDD electrode, the electron transfer resistance is lower on this new electrode. Compared to an electrode without Au-NPs, the peak potential is negatively shifted by 42 mV, and the peak current is increased by 55 %. This is ascribed to the larger surface in the AuNP-CS nanocomposite which improves the adsorption of AChE, enhances its activity, and facilitates electrocatalysis. Under optimum conditions, the inhibitory effect of chlorpyrifos is linearly related to the negative log of its concentration in the 10−11 to 10−7 M range, with a detection limit of 1.3 × 10−13 M. For methyl parathion, the inhibition effect is linear in the 10−12 to 10−6 M range, and the detection limit is 4.9 × 10−13 M. The biosensor exhibits good precision and acceptable operational and temporal stability.
TL;DR: In this article, a metal-organic framework sustained by a nanosized Ag12 cuboctahedral node was applied to selectively extract traces of lead(II) ion from environmental water samples.
Abstract: We show that a metal-organic framework (MOF) sustained by a nanosized Ag12 cuboctahedral node can be applied to selectively extract traces of lead(II) ion from environmental water samples. The MOF was characterized by thermogravimetric and differential thermal analysis, scanning electron microscopy, FTIR, and X-ray diffraction. The effects of pH value, flow rates, of type, concentration and volume of the eluent, of break-through volume and potentially interfering ions on the separation and determination of lead were evaluated. Following desorption with EDTA, Pb(II) was quantified by FAAS. The use of the MOF results in excellent analytical figures of merit including an analytical range from 2 to 180 μg L−1 of Pb(II) (R2 > 0.99); a limit of detection of 500 ng L−1; an adsorption capacity of 120 mg g−1; an extraction efficiency of >95 %, and a relative standard deviation of <4 % (for eight separate column experiments).
TL;DR: In this paper, Fe3O4 nanoparticles were deposited on sheets of graphene oxide (GO) by a precipitation method, and glucose oxidase (GOx) was then immobilized on this material to produce a GOx/Fe 3O4/GO magnetic nanocomposite containing crosslinked enzyme clusters.
Abstract: Fe3O4 nanoparticles were deposited on sheets of graphene oxide (GO) by a precipitation method, and glucose oxidase (GOx) was then immobilized on this material to produce a GOx/Fe3O4/GO magnetic nanocomposite containing crosslinked enzyme clusters. The 3-component composite functions as a binary enzyme that was employed in a photometric method for the determination of glucose and hydrogen peroxide where the GOx/Fe3O4/GO nanoparticles cause the generation of H2O2 which, in turn, oxidize the substrate N,N-diethyl-p-phenylenediamine to form a purple product with an absorption maximum at 550 nm. The absorbance at 550 nm can be correlated to the concentration of glucose and/or hydrogen peroxide. Under optimized conditions, the calibration plot is linear in the 0.5 to 600 μM glucose concentration range, and the detection limit is 0.2 μM. The respective plot for H2O2 ranges from 0.1 to 10 μM, and the detection limit is 0.04 μM. The method was successfully applied to the determination of glucose in human serum samples. The GOx/Fe3O4/GO nanoparticles are reusable.
TL;DR: An overview on microbead-based platforms for biosensing with a main focus on nucleic acid detection and the relevance and trends of the methods in terms of high-level multiplexed analysis and their potential in diagnosis and personalized medicine are discussed.
Abstract: Microbead-based technologies represent elegant and versatile approaches for highly parallelized quantitative multiparameter assays. They also form the basis of various techniques for detection and quantification of nucleic acids and proteins. Nucleic acid-based methods include hybridization assays, solid-phase PCR, sequencing, and trapping assays. Microbead assays have been improved in the past decades and are now important tools in routine and point-of-care diagnostics as well as in life science. Its advances include low costs, low workload, high speed and high-throughput automation. The potential of microbead-based assays therefore is apparent, and commercial applications can be found in the detection and discrimination of single nucleotide polymorphism, of pathogens, and in trapping assays. This review provides an overview on microbead-based platforms for biosensing with a main focus on nucleic acid detection (including amplification strategies and on selected probe systems using fluorescent labeling). Specific sections cover chemical properties of microbeads, the coupling of targets onto solid surfaces, microbead probe systems (mainly oligonucleotide probes), microbead detection schemes (with subsections on suspension arrays, microfluidic devices, and immobilized microbeads), quantification of nucleic acids, PCR in solution and the detection of amplicons, and methods for solid-phase amplification. We discuss selected trends such as microbead-coupled amplification, heterogeneous and homogenous DNA hybridization assays, real-time assays, melting curve analysis, and digital microbead assays. We finally discuss the relevance and trends of the methods in terms of high-level multiplexed analysis and their potential in diagnosis and personalized medicine. Contains 211 references.
TL;DR: In this article, the authors reported the synthesis of Fe3O4-functionalized metal-organic framework (m-MOF) composite from Zn(II) and 2-aminoterephthalic acid by a hydrothermal reaction.
Abstract: We report on the synthesis of Fe3O4-functionalized metal-organic framework (m-MOF) composite from Zn(II) and 2-aminoterephthalic acid by a hydrothermal reaction. The magnetic composite is iso-reticular and was characterized by FTIR, X-ray diffraction, SEM, magnetization, and TGA. The m-MOF was then applied as a sorbent for the solid-phase extraction of trace levels of copper ions with subsequent quantification by electrothermal AAS. The amount of sorbent applied, the pH of the sample solution, extraction time, eluent concentration and volume, and desorption time were optimized. Under the optimum conditions, the enrichment factor is 50, and the sorption capacity of the material is 2.4 mg g−1. The calibration plot is linear over the 0.1 to 10 μg L−1 Cu(II) concentration range, the relative standard deviation is 0.4 % at a level of 0.1 μg L−1 (for n = 10), and the detection limit is as low as 73 ng L−1. We consider this magnetic MOF composite to be a promising and highly efficient material for the preconcentration of metal ions.
TL;DR: In this article, a host-guest interaction between a deoxy-(2-aminoethylamino)-β-cyclodextrin (CD) bound to graphene nanosheets and the Cu(II) complexes of the tryptophan (Trp) enantiomers via a ligand exchange mechanism was investigated.
Abstract: We report on a method for electrochemical enantioselective recognition of tryptophan (Trp) enantiomers. It is based on competitive host-guest interaction between a deoxy-(2-aminoethylamino)-β-cyclodextrin (CD) bound to graphene nanosheets and the Cu(II) complexes of the Trp enantiomers via a ligand exchange mechanism. Chiral recognition was investigated via cyclic voltammetry and electrochemical impedance spectroscopy. The results reveal that the CD bound to graphene displays a stronger interaction with the Cu(II) complex of L-Trp than to that of D-Trp. The method was applied to the determination of the ratio of Trp enantiomers in mixtures.
TL;DR: In this article, it was shown that the very weak chemiluminescence (CL) of the Ce(IV)-thiosulfate system is enhanced by a factor of ~150 in the presence of fluorescent carbon dots (C-dots).
Abstract: We show that the very weak chemiluminescence (CL) of the Ce(IV)-thiosulfate system is enhanced by a factor of ~150 in the presence of fluorescent carbon dots (C-dots). The C-dots were prepared by a solvothermal method and characterized by fluorescence spectra and transmission electron microscopy. Possible mechanisms that lead to the effect were elucidated by recording fluorescence and CL spectra. It is found that dopamine at even nanomolar levels exerts a diminishing effect on the enhancement of CL. This was exploited to design a method for the determination of dopamine in the concentration range from 2.5 nM to 20 μM, with a limit of detection (at 3 s) of 1.0 nM. Dopamine was determined by this method in spiked human plasma samples with satisfactory results.
TL;DR: The kinetics of the increase in fluorescence for each of the qPCR monitoring chemistries form six groups with distinct fluorescence kinetics with respect to the input of both ds-DNA and ss-cDNA are determined.
Abstract: The analysis of quantitative PCR data usually does not take into account the fact that the increase in fluorescence depends on the monitoring chemistry, the input of ds-DNA or ss-cDNA, and the directionality of the targeting of probes or primers. The monitoring chemistries currently available can be categorized into six groups: (A) DNA-binding dyes; (B) hybridization probes; (C) hydrolysis probes; (D) LUX primers; (E) hairpin primers; and (F) the QZyme system. We have determined the kinetics of the increase in fluorescence for each of these groups with respect to the input of both ds-DNA and ss-cDNA. For the latter, we also evaluated mRNA and cDNA targeting probes or primers. This analysis revealed three situations. Hydrolysis probes and LUX primers, compared to DNA-binding dyes, do not require a correction of the observed quantification cycle. Hybridization probes and hairpin primers require a correction of −1 cycle (dubbed C-lag), while the QZyme system requires the C-lag correction and an efficiency-dependent C-shift correction. A PCR efficiency value can be derived from the relative increase in fluorescence in the exponential phase of the amplification curve for all monitoring chemistries. In case of hydrolysis probes, LUX primers and hairpin primers, however, this should be performed after cycle 12, and for the QZyme system after cycle 19, to keep the overestimation of the PCR efficiency below 0.5 %.
TL;DR: In this paper, a magnetic multwalled carbon nanotubes functionalized with 8-aminoquinoline was applied to the preconcentration of Cd(II), Pb(II) and Ni(II).
Abstract: We report that magnetic multiwalled carbon nanotubes functionalized with 8-aminoquinoline can be applied to the preconcentration of Cd(II), Pb(II) and Ni(II) ions. The parameters affecting preconcentration were optimized by a Box-Behnken design through response surface methodology. Three variables (extraction time, magnetic sorbent amount, and pH value) were selected as the main factors affecting sorption, and four variables (type, volume and concentration of the eluent; elution time) were selected for optimizing elution. Following sorption and elution, the ions were quantified by FAAS. The LODs are 0.09, 0.72, and 1.0 ng mL−1 for Cd(II), Ni(II), and Pb(II) ions, respectively. The relative standard deviations are <5.1 % for five separate batch determinations at 30 ng mL−1 level of Cd(II), Ni(II), and Pb(II) ions. The sorption capacities (in mg g−1) of this new sorbent are 201 for Cd(II), 150 for Pb(II), and 172 Ni(II). The composite was successfully applied to the rapid extraction of trace quantities of heavy metal ions in fish, sediment, soil, and water samples.
TL;DR: A sensitive method based on competitive interaction between non-labeled specific primary antibodies and target antigens in a sample and in the test zone of a membrane and detection of the immune complexes on the membrane by using a secondary antibodies labeled with gold nanoparticles is described.
Abstract: We describe a sensitive method for the immunochromatographic determination of aflatoxin B1. It is based on the following steps: 1) Competitive interaction between non-labeled specific primary antibodies and target antigens in a sample and in the test zone of a membrane; 2) detection of the immune complexes on the membrane by using a secondary antibodies labeled with gold nanoparticles. The method enables precise adjustment of the required quantities of specific antibodies and the colloidal (gold) marker. It was applied in a lateral flow format to the detection of aflatoxin B1 and exhibits a limit of detection (LOD) of 160 pg · mL−1 if detected visually, and of 30 pg · mL−1 via instrumental detection. This is significantly lower than the LOD of 2 ng · mL−1 achieved by conventional lateral flow analysis using the same reagents.