Showing papers on "Detection limit published in 2020"

3D-Printed graphene/polylactic acid electrode for bioanalysis: Biosensing of glucose and simultaneous determination of uric acid and nitrite in biological fluids

Abstract: Additive manufacturing, also known as 3D-printing, is receiving great interest by chemists due to the easy design of novel materials, fast prototyping and reducing waste, which enables large-scale fabrication of electrochemical devices. Herein we demonstrate the development of (bio)sensors for the analysis of biological fluids using 3D-printing. Fused deposition modelling was used to fabricate (bio)sensing platforms from commercially-available filaments made of polylactic acid containing graphene (G-PLA). An enzymatic glucose biosensor fabricated on the G-PLA surface was developed and applied for glucose sensing in blood plasma using chronoamperometry. Oxygenated groups from the polymeric matrix provides suitable condition to enzyme immobilization by crosslinking with glutaraldehyde. The biosensor presented a limit of detection (LOD) of 15 μmol L−1, inter-day and intra-day precision lower than 5 %, and adequate recovery values (90–105 %) for the analysis of plasma. We also show that the surface treatment of the 3D-printed sensor (mechanical polishing followed solvent immersion) provides improved electrochemical properties for the direct detection of nitrite and uric acid. Differential-pulse voltammetry and multiple-pulse amperometry under flow conditions were evaluated and compared for the determination of both species in saliva and urine. Highlights are presented for the amperometric detection within a linear range from 0.5–250 μmol L−1 for both analytes, LODs of 0.02 and 0.03 μmol L−1 for uric acid and nitrite, respectively, and high precision (RSD

Platinum Nanozyme-Triggered Pressure-Based Immunoassay Using a Three-Dimensional Polypyrrole Foam-Based Flexible Pressure Sensor

Abstract: This work describes a novel and portable pressure-based point-of-care (POC) testing strategy for the sensitive and rapid detection of carcinoembryonic antigen (CEA) via a flexible pressure sensor constructed by three-dimensional (3D) polypyrrole (PPy) foam. Initially, platinum nanoparticles (PtNPs) were conjugated to the detection antibodies, which were used to form sandwich-type immunocomplexes with targets and capture antibodies in the reaction cell. Then, the carried PtNPs catalyzed the dissociation of hydrogen peroxide (H2O2) for the generation of oxygen (O2) in a sealed device, translating the biomolecule recognition event into gas pressure. With the increase of pressure, a flexible pressure sensor with 3D polypyrrole foam as the sensing layer was used to sensitively monitor the pressure variations in this system. Thus, the concentration of the target could be quantitatively determined by the pressure response. Under optimal conditions, the pressure-based immunosensor showed good sensing performance for CEA in the dynamic working range from 0.2 to 60 ng/mL with a detection limit of 0.13 ng/mL. The reproducibility, specificity, and accuracy compared with commercial enzyme-linked immunosorbent assay (ELISA) kit were also acceptable. Therefore, this work provides a promising approach for developing portable and sensitive POC testing in the future.

Bipyridine- and Copper-Functionalized N-doped Carbon Dots for Fluorescence Turn Off–On Detection of Ciprofloxacin

Abstract: Herein, a fluorescence turn off-on nanosensor has been successfully developed using functionalized N-doped carbon dots (N-CDs) as the label-free sensing probe for the ultrasensitive detection of Cu2+ ions first and then ciprofloxacin (CIP), one of the most commonly used antibiotics for disease control, in the presence of bipyridine The homogeneous and narrowly distributed N-CDs with a mean size of 57 nm and a high quantum yield of 84% are fabricated via the hydrothermal method in the presence of citric acid and ethylenediamine as the carbon and nitrogen sources, respectively The Cu2+ ions serve as both analyte and fluorescence quenchers in the sensing platform of N-CDs, and a good linear response to Cu2+ in the range of 001-035 μM with a limit of detection (LOD) of 0076 nM is observed Then, 035 μM Cu2+ is used as the fluorescence quencher of N-CDs to build up the fluorescence turn off-on sensing probe for the detection of CIP using bipyridine (bipy) as the linker for CIP and Cu2+ ions The addition of CIP to the bipy-Cu@N-CD composites triggers the formation of CIP-bipy-Cu conjugate as well as the release of N-CDs, resulting in the recovery of fluorescence intensity after 6 min of incubation The sensing probe exhibits a two-phase linear response to CIP in the concentration range of 005-1 and 1-50 μM with a LOD of 04 nM In addition, the bipy-Cu@N-CD probe shows high sensitivity toward CIP over the 19 other interferences Good recovery of 96-110% is also observed when 01-09 μM CIP is spiked into the real samples Results obtained in this study clearly demonstrate a newly developed sensing platform with rapid detection of metal ions and antibiotics, which can open an avenue to develop highly efficient and robust sensing probes for the detection of metal ions, organic metabolites, and biomarkers in biological applications

SERS-Active MIL-100(Fe) Sensory Array for Ultrasensitive and Multiplex Detection of VOCs.

Abstract: The application of metal-organic frameworks (MOFs) as SERS-active platforms in multiplex volatile organic compounds (VOCs) detection is still unexplored. Herein, we demonstrate that MIL-100 (Fe) serves as an ideal SERS substrate for the detection of VOCs. The limit of detection (LOD) of MIL-100(Fe) for toluene sensing can reach 2.5 ppm, and can be even further decreased to 0.48 ppb level when "hot spots" in between Au nanoparticles are employed onto MIL-100 (Fe) substrate, resulting in an enhancement factor of 1010 . Additionally, we show that MIL-100(Fe) substrate has a unique "sensor array" property allowing multiplex VOCs detection, with great modifiability and expandability by doping with foreign metal elements. Finally, the MIL-100(Fe) platform is utilized to simultaneously detect the different gaseous indicators of lung cancer with a ppm detection limit, demonstrating its high potential for early diagnosis of lung cancer in vivo.

Two-dimensional Cd-doped porous Co3O4 nanosheets for enhanced room-temperature NO2 sensing performance

Abstract: P-type Co3O4 has received ever-growing interest as a promising gas-sensing material due to the unique advantages of low-cost, earth abundance and considerable electrical conductivity at relatively low temperature. Herein, we designed and fabricated two-dimensional (2D) Cd-doped porous Co3O4 nanosheets through a microwave-assisted solvothermal method and subsequently in-situ annealing process. It is found that as-prepared 5 %-Cd-Co3O4-based gas sensor shows a significantly improved response value of 3.38 (Ra/Rg) and a relatively lower recovery time of 620 s for NO2 detection at room temperature (25 °C). Additionally, the sensor displays a wide detection range for NO2 detection low to 154 ppb (low theoretical limit of detection), outstanding selectivity compared with some volatile organic compounds, and excellent long-term stability for 6 months. The results of experiments and the corresponding Lewis acid-base theory reveal that the excellent room-temperature sensing performance is mainly promoted by the Cd dopant through a combined set of factors, including enhanced electronic conductivity, increased oxygen vacancy concentration and formed Co2+−O2− to improve NO2 adsorption. However, the further increased concentration of Cd2+ as Lewis acid sites will decrease the adsorption of NO2 that can benefit for improving recovery performance. Thus, the demonstration of such 2D Cd-doped porous Co3O4 nanosheets provides valuable insights for the p-type metal oxide semiconductor-based room-temperature gas sensors.

Validated electrochemical immunosensor for ultra-sensitive procalcitonin detection: Carbon electrode modified with gold nanoparticles functionalized sulfur doped MXene as sensor platform and carboxylated graphitic carbon nitride as signal amplification

Abstract: Septicemia, also known as sepsis, refers to a systemic inflammatory response syndrome and becomes the dominant reason of mortality for seriously diseases. Procalcitonin (PCT), the peptide precursor of the hormones, is a key biomarker of septicemia in the diagnosis and detection of bacterial inflammation. In this study, an ultra-sensitive sandwich type electrochemical immunosensor for PCT detection was constructed. Firstly, delaminated sulfur-doped MXene (d-S-Ti3C2TX MXene) modified glassy carbon electrode (GCE) including gold nanoparticles (AuNPs) was utilized as immunosensor platform to increase the amount of PCT antibody1 (Ab1). After that, carboxylated graphitic carbon nitride (c-g-C3N4) was used to label PCT Ab2 as signal amplification. The structure of electrochemical immunosensor was highlighted by x-ray diffraction (XRD) method, scanning electron microscope (SEM), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Herein, c-g-C3N4 not only has excellent catalytic activity toward H2O2 for signal amplification, but also can be directly utilized as redox probe. The analytical results have revealed that 0.01 - 1.0 pg mL-1 and 2.0 fg mL-1 were found as linearity range and limit of detection (LOD). Furthermore, the validated electrochemical immunosensor was examined in terms of stability, repeatability, reproducibility and reusability. Finally, the immunosensor was applied to plasma samples having high recovery.

Visible light activated excellent NO2 sensing based on 2D/2D ZnO/g-C3N4 heterojunction composites

Abstract: In this work, 2D/2D ZnO/g-C3N4 heterojunction composite was synthesized through an ultrasonic mixing and subsequent calcination process. The gas-sensing performance to NO2 was investigated at room temperature activated by visible/ultra-violet LED light sources. Noticeably, when ZnO/g-C3N4 composite is illuminated by 460 nm light, it exhibits the highest response of 44.8 to 7 ppm NO2, and the response and recovery time is 142 and 190 s, respectively. Furthermore, it possesses excellent repeatability and selectivity to NO2, and the limit of detection is 38 ppb. In addition, the effect of humidity on the sensing performance under visible light was also investigated. The excellent gas-sensing performance is attributed to the absorbance of g-C3N4 in the visible light region and the charge separation at the interface between ZnO and g-C3N4.

An ultrasensitive hybridization chain reaction-amplified CRISPR-Cas12a aptasensor for extracellular vesicle surface protein quantification.

Abstract: Tumor-derived extracellular vesicle (TEV) protein biomarkers facilitate cancer diagnosis and prognostic evaluations. However, the lack of reliable and convenient quantitative methods for evaluating TEV proteins prevents their clinical application. Methods: Here, based on dual amplification of hybridization chain reaction (HCR) and CRISPR-Cas12a, we developed the apta-HCR-CRISPR assay for direct high-sensitivity detection of TEV proteins. The TEV protein-targeted aptamer was amplified by HCR to produce a long-repeated sequence comprising multiple CRISPR RNA (crRNA) targetable barcodes, and the signals were further amplified by CRISPR-Cas12a collateral cleavage activities, resulting in a fluorescence signal. Results: The established strategy was verified by detecting the TEV protein markers nucleolin and programmed death ligand 1 (PD-L1). Both achieved limit of detection (LOD) values as low as 102 particles/µL, which is at least 104-fold more sensitive than aptamer-ELISA and 102-fold more sensitive than apta-HCR-ELISA. We directly applied our assay to a clinical analysis of circulating TEVs from 50 µL of serum, revealing potential applications of nucleolin+ TEVs for nasopharyngeal carcinoma cancer (NPC) diagnosis and PD-L1+ TEVs for therapeutic monitoring. Conclusion: The platform was simple and easy to operate, and this approach should be useful for the highly sensitive and versatile quantification of TEV proteins in clinical samples.

Fabrication of novel polymer-modified graphene-based electrochemical sensor for the determination of mercury and lead ions in water and biological samples

Abstract: This paper presents the application of polyglycine-modified graphene paste electrode (PGMGPE) for the electrochemical detection of Hg (II) and Pb (II) ions in the water and biological samples. The developed electrode was characterized by field emission scanning electron microscopy. Electrochemical techniques such as cyclic voltammetry and differential pulse voltammetry were used to study the behavior of metal ions. The modification process improves the electrochemical behavior of heavy metal ions. The peak current varied linearly with the increase of the concentration leading to a detection limit of 6.6 μM (Hg (II)) and 0.8 μM (Pb (II)), respectively. The developed electrode exhibits good sensitivity, selectivity, stability, and lower detection limit, and was successfully applied to the determination of heavy metal ions in water and biological samples with a good recovery range.

Layer-by-layer assembly of magnetic-core dual quantum dot-shell nanocomposites for fluorescence lateral flow detection of bacteria

Abstract: Lateral flow immunoassay (LFA) strips are extensively used for rapid tests of various biochemical molecules, but these strips still have some limitations in bacterial detection due to their low sensitivity and poor stability in complex samples. In this study, we reported a highly sensitive and quantitative fluorescent LFA strip for bacterial detection by using novel magnetic-core@dual quantum dot (QD)-shell nanoparticles (Fe3O4@DQDs) as multifunctional fluorescent labels. The Fe3O4@DQDs were prepared through a polyethyleneimine (PEI)-mediated layer-by-layer (LBL) assembly method, and they possess monodispersity, high magnetic responsiveness, good stability, and superior fluorescence properties. Based on these merits, the Fe3O4@DQDs were used to capture and enrich bacteria from complex samples and then used as advanced fluorescent labels of LFA strips for the quantitative detection of bacteria. Under optimal conditions, the assay ultra-sensitively detected Streptococcus pneumoniae with a low limit of detection of 8 cells per mL and a wide dynamic linear range of 10 cells per mL to 107 cells per mL. Systematic comparison revealed that the fluorescence detection limit of the Fe3O4@DQD-based strip was 55 and 1000 times higher than those of Fe3O4-core@QD-shell nanocomposite (Fe3O4-QD)-based and conventional QD microsphere-based strips, respectively. The proposed method also exhibited high specificity and selectivity for biological samples (human whole blood and sputum) and is thus a promising tool for real bacterial sample testing.

Functionalized carbon quantum dots as fluorescent nanoprobe for determination of tetracyclines and cell imaging.

Abstract: Nitrogen and sulfur co-doped carbon dots (N, S-CQDs) with high fluorescent, water-soluble, low-toxicity properties were synthesized by microwave-assisted hydrothermal approach. The prepared N, S-CDs exhibited high selectivity in detection of tetracyclines (TCs) and displayed a fast-responsive fluorescence quenching signal in the mixture, which are mainly attributed to the inner filter effect (IFE). The synthesized N, S-CQDs are successfully used as a fluorescent nanoprobe for the determination of CTC in milk samples (with excitation/emission maxima at 373/424 nm). The limit of detection (LOD) is 71 ng mL−1, and the recoveries of spiked samples range from 96 to 104% with a relative standard deviations (RSDs) less than 2.7% (n = 3). Additionally, the cytotoxicity and optical imaging performance of N, S-CQDs were preliminarily evaluated. The results indicate the low-toxicity and good biocompatibility of the N, S-CQDs and their promising future as fluorescent-imaging agents in pharmaceutical analysis.