Concentration Of Target Analyte Research Articles

Ferric hydroxide nanocage triggered Fenton-like reaction to improve amperometric immunosensor

Abstract A new immunoprobe based on ferric hydroxide nanocage (Fe(OH)3-NC) was designed to construct an amperometric immunosensor to detect tumour marker. Using the sacrificial template method, the Fe(OH)3-NC was facilely synthesized according to Pearson’s hard and soft acid-base principle. The immunoprobe was fabricated by immobilizing antibodies on reduced graphene oxide-Au composite combined with Fe(OH)3-NC. Fenton-like reaction can be triggered by Fe(OH)3-NC to degrade the methylene blue molecules fixed in the substrate of electrode, resulting in the decrease of current signal which had correlation with the concentration of target analyte. Dissimilar to other Fenton and Fenton-like catalysts with dependence of strong acid or poor molecule-accessibility, the as-prepared Fe(OH)3-NC had more reachable catalytic sites due to its composition and incompact structure. Therefore, the analytical performance of the immunosensor was remarkably enhanced. Under optimal conditions, the immunosensor exhibited an improved performance for CA 19-9, a model analyte, in a wide linear range from 0.00001 to 100 U mL−1 and an ultra-low detection limit of 0.785 μU mL−1. For serum sample, this immunosensor demonstrated excellent consistency with electrochemiluminescence. This work will be of significance in designing new Fenton and Fenton-like catalysts for electrochemical immunosensors.

Smart materials for sample preparation in bioanalysis: A green overview

The analysis of biological samples is a complex challenge due to the complexity of the matrix, but also to the low concentration of target analytes that must be determined. Consequently, different sample treatment procedures have been proposed in bioanalysis to clean-up and enrich sample extracts, paying special attention to microextraction approaches. In this frame, the combined use of microextraction approaches with smart materials provides environmentally friendly sample treatment strategies with improved selectivity, sensitivity, and reusability. Applications of smart solid materials includes antibody–antigen interaction based materials, aptamers, molecularly imprinted polymers, metal organic frameworks, restricted access materials, carbon based nanomaterials, and magnetic nanoparticles. On the other hand, smart liquid materials used in sample preparation in bioanalysis comprise bio-based solvents, supramolecular solvents, ionic liquids, and deep eutectic solvents. Synthesis and applications of smart materials have been discussed under a Green Analytical Chemistry perspective.

Inkjet-printed paper-based colorimetric sensor coupled with smartphone for determination of mercury (Hg2+)

We report an inkjet-printed paper based colorimetric sensor with silver nanoparticles (AgNPs) using smartphone and color detector App for on-site determination of mercuric ion (Hg2+) from environmental water samples. The AgNPs printed on Whatman filter paper (No. 1) is employed for detection of Hg2+ which is reliant on the color change of NPs from yellow to discoloration depending on the concentration of target analyte in sample solution. The quantitative determination was performed by calculating the signal intensity of AgNPs on printed paper substrate after the introduction of Hg2+ using smartphone and RGB color detector. The mechanism for detection of Hg2+ on paper substrate is verified using UV-Vis spectrophotometry (UV-Vis), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS) and basic chemical assays. The linear range acquired for paper based colorimetric detection in the range of 40–1200 µgL−1 with limit of detection of 10 µgL−1. The results obtained using an inkjet-printed paper-based chemical sensor combined with a smartphone is validated with data of inductively coupled plasma-atomic emission spectroscopy (ICP-AES) measurement. The advantages of paper based detection are simple, rapid, economic and can be applied at the sample sources for determination of Hg2+.

Synthesis, structural analysis, electrochemical and antimicrobial activities of copper magnesium zirconosilicate (Cu20Mg10Si40Zr(30-x)O:(x = 0,5,7,10) Ni2+) nanocrystals

A complex sol-gel method for synthesizing structurally controlled copper magnesium zirconosilicate catalysts supported with Ni2+ nano-particles with a surface area of 21.62538–25.37952 m2 g−1 and the particle sizes from 47.04 nm to 41.11 nm. The XRD and TEM results demonstrate that Ni2+-crystallinity promotes an important role in (Cu20Mg10Si40Zr(30-x) O:(x = 0, 5, 7,10) Ni2+) formation. The chemical states of elements are investigated using the X-ray photoelectron spectroscopy (XPS). The biological activities of fabricated antiseptics nanoconjugates were investigated against some pathogenic microbes. The effective dose of each studied antiseptic was determined. The toxicity performance of each antiseptic nanoconjugate was measured. Here, for the fabrication of the proposed electrochemical sensor to selective 3-methoxyphenylhydrazine (3-MPHyd), the synthesized Cu20Mg10Si40Zr(30-x)O:(x = 0, 5, 7,10) Ni2+ was exposed to coat the glassy carbon electrode (GCE). 5% Nafion conducting polymer as adhesive was used to coat the prepared material onto the GCE. The calibration of the sensor was performed by plotting a linear relation measured (R2 = 0.9964) as current versus target analyte concentration. The sensitivity (76.193 µAµM−1cm−2) of the sensor is calculated from the slope of calibration curve divided by the active surface area of GCE (0.0316 cm2). The linear dynamic range (LDR; 0.01 nM to 1.0 pM) is used calculated the sensor analytical parameters. Applying the signal-to-noise ratio at 3, the lower limit of detection (0.93 ± 0.05 pM) is calculated. From the results acquired of antimicrobial potential of all fabricated nanoconjugates, it can be discovered the lethal dose that could be killed all log cell count of S1 antiseptic nanoconjugate was 75.0 mg/L for E. coli after 10 min of contact time and 15 min for Staphylococcus aureus, while the fungal species did not completely removed. On the other side the lethal dose of S3 nanoconjugate was 50.0 mg/L for E. coli, 75.0 mg/L for other tested microbes. The fabricated sensor reliability parameters such as reproducibility, stability, linearity, and response time are found good and satisfactory. Furthermore, the proposed fabricated sensor was used to detect the target 3-MPHyd significantly by electrochemical method in the real samples.

Programmable microfluidic flow for automatic multistep digital assay in a single-sheet 3-dimensional paper-based microfluidic device

A single-sheet 3-dimensional paper-based microfluidic analytical device (3D-μPAD) has a user-friendly compact format that eliminates any potential for user alignment error compared to the stacking and folding format. However, achieving sophisticated analysis is still a challenge because forming a complex 3D microfluidic network sufficient for performing analysis in a single sheet of paper is difficult. Here, we present the first report of automatic multistep digital analysis in a single-sheet 3D-μPAD created by controlling the penetration of different wax inks into paper. Simple printing of different wax inks with different spreading properties produces different dimension microchannels in paper. This controllable change in the dimensions of the microchannels results in different flow rates of fluid in each microchannel. Based on the spatial resolution of the microchannels, our strategy enables programming of microfluidic flow through manipulation of the fluidic time delay. This approach creates 3D-μPADs capable of sequential fluid delivery and multistep biochemical reactions with single loading of a sample solution. The methodology can be further expanded to combination with digital assays to measure the concentration of a target analyte by simply counting the number of colored bars at a fixed time. It does not require any external instruments to analyze the measurement of the target analyte concentration. The significance of this work lies in the promising potential for automatic multistep digital assays in a low-cost and easy-to-use paper-based format that can be integrated with a roll-to-roll process for commercial-scale manufacturing.

Electrochemical Immunosensor for the Early Detection of Rheumatoid Arthritis Biomarker: Anti-Cyclic Citrullinated Peptide Antibody in Human Serum Based on Avidin-Biotin System.

Rheumatoid arthritis (RA) is a chronic autoimmune disease that produces a progressive inflammatory response that leads to severe pain, swelling, and stiffness in the joints of hands and feet, followed by irreversible damage of the joints. The authors developed a miniaturized, label-free electrochemical impedimetric immunosensor for the sensitive and direct detection of arthritis Anti-CCP-ab biomarker. An interdigitated-chain-shaped microelectrode array (ICE) was fabricated by taking the advantage of microelectromechanical systems. The fabricated ICE was modified with a self-assembled monolayer (SAM) of Mercaptohexanoic acid (MHA) for immobilization of the synthetic peptide bio-receptor (B-CCP). The B-CCP was attached onto the surface of SAM modified ICE through a strong avidin-biotin bio-recognition system. The modified ICE surface with the SAM and bio-molecules (Avidin, B-CCP, Anti-CCP-ab and BSA) was morphologically and electrochemically characterized. The change in the sensor signal upon analyte binding on the electrode surface was probed through the electrochemical impedance spectroscopy (EIS) property of charge-transfer resistance (Rct) of the modified electrodes. EIS measurements were target specific and the sensor response was linearly increased with step wise increase in target analyte (Anti-CCP-ab) concentrations. The developed sensor showed a linear range for the addition of Anti-CCP-ab between 1 IU mL−1 → 800 IU mL−1 in phosphate buffered saline (PBS) and Human serum (HS), respectively. The sensor showed a limit of detection of 0.60 IU mL−1 and 0.82 IU mL−1 in the PBS and HS, respectively. The develop bio-electrode showed a good reproducibility (relative standard deviation (RSD), 1.52%), selectivity and stability (1.5% lost at the end of 20th day) with an acceptable recovery rate (98.0% → 101.18%) and % RSD’s for the detection of Anti-CCP-ab in spiked HS samples.

Dynamically controlling the electrode potential of a microbial fuel cell-powered biocathode for sensitive quantification of nitrate

Microbial fuel cell (MFC) powered biocathode sensors are promising for self-powered monitoring of water contaminants. However, the extensive electrode potential fluctuation would occur when the MFC powered biocathode were used for detecting different concentrations of target analytes, which in turn limits the sensitivity and accuracy. To address this, for the first time, an electrokinetic model for the nitrate reduction by an MFC powered biocathode was developed. Interestingly, both the theoretical simulation and experimental results disclosed an optimal external resistance, under which the biocathode potential was dynamically controlled in the range that electron transfer from the electrode to the nitrate though biocathodic reduction was kinetically saturated, and the output current was exclusively nitrate concentration depended. With this basis, an MFC powered biocathode sensor was for the first time developed, which showed an extremely low limit of detection (0.11 μM) and wide linear detection range (1–500 μM) in nitrate detection. Moreover, this biosensing system also exhibited good reusability and excellent reliability in complex wastewater environment. This work developed an MFC powered biocathode sensing system with excellent nitrate detection capacity, and demonstrated a novel strategy to accurately quantify the target analytes with dynamically controllable electrode potential.

Microwave absorption medium-assisted extraction coupled with reversed-phase dispersive liquid-liquid microextraction of triazine herbicides in corn and soybean samples.

A new extraction method, microwave absorption medium-assisted extraction coupled with reversed-phase dispersive liquid-liquid microextraction, was developed for the determination of triazine herbicides in corn and soybean samples. Triazine herbicides were extracted with hexane and then directly enriched into the ionic liquid phase. The purification of sample and concentration of target analytes were performed simultaneously. The method combines the advantages of nonpolar solvent dynamic microwave extraction and reversed-phase dispersive liquid-liquid microextraction, which could greatly simplify the operation and reduce the whole pretreatment time. The Box-Behnken design was used to the optimization of experimental factors involved in the dynamic microwave-assisted extraction. In the present study, good linearity in the range of 5.00-500.00µg/kg was obtained. The limits of detection and quantification varying from 1.3 to 4.2 and 4.1 to 13.9µg/kg were achieved, respectively. The intra- and interday precisions were between 2.7 and 6.9%. The present method was applied to the analysis of corn and soybean samples, and the recoveries of analytes ranged from 80.7 to 106.9% with the relative standard deviations of 2.1-7.8%. The present method shows the potentials of practical applications in the treatment of the complex fatty solid samples.

Colorimetric determination of L-cysteine in milk samples with surface functionalized silver nanoparticles

A simple, selective and sensitive method is proposed for determination of cysteine (Cys) in milk samples using ionic liquid functionalized silver nanoparticles (ILs-AgNPs) as a colorimetric probe. ILs-AgNPs was synthesized by simple reduction method using silver nitrate as a precursor and sodium borohydride as a reducing agent and functionalized with ILs to prevent particles from self-aggregation. The sensing mechanism has been dependent on the color change of ILs-AgNPs and red shift of absorption band from 395nm to 560nm in the visible region, which is found proportional to the concentration of target analyte in sample. ILs-AgNPs was characterized in absence and presence of Cys by UV-vis, Fourier transform-infrared (FTIR) spectroscopy, transmission electron microscope (TEM) and dynamic light scattering (DLS). The linear range was acquired in the range of 0-100ngmL-1, with correlation coefficient (R2) of 0.996 and limit of detection (LOD) of 4.0nM. The binding mechanism and interactions between Cys and ILs-AgNPs was confirmed by calculating the binding constant and thermodynamic parameters such as enthalpy (∆H), entropy (∆S) and Gibb's free energy (∆G). The use of ILs-AgNPs exhibited high colorimetric selectivity for Cys in milk samples in presence of other amino acids. This proposed strategy possessed the advantages of simplicity and selectivity, hence is applied for analysis of Cys in milk samples.

Endophytic fungi-based biosensors for environmental contaminants-A perspective

Nature's degradation and environmental concerns have triggered the enormous interest among the researchers to pursue a sustainable solution for environmental monitoring. Combining biotechnology and analytical techniques encourage developing advanced biosensors to significantly improve the environmental monitoring at a lower cost. Herein, we made an effort to shed some light on endophytic fungi in biosensing applications based on optical and electrochemical detection signal mechanisms. Biosensors are hybrid devices that can generate specific qualitative or quantitative sensing signal about target analyte concentration (such as heavy metal or chemical toxicant in a sample) by integrating biological or biomimetic detection element with the physical/chemical transducer. There are only a few studies reported for the endophytes application in biosensor, which we have summarized in the current perspective. Concisely, endophytes are rich sources of metabolites that can be utilized for the biogenic synthesis of nanoparticles which can be further incorporated in sensing devices. In addition, the enzymatic extracts of endophytic fungi can be directly applied as bio-receptors upon immobilization. The studies on the endophytic fungi based sensing element indicates its potential use for efficient monitoring and treatment of emerging contaminants in the environment.

Coulometry-assisted quantitation in spray ionization mass spectrometry.

The concentration of target analyte in a mixture can be quantified by combining coulometric measurements with spray ionization mass spectrometry. A three-electrode system screen printed on the polymer support acts both as the coulometry platform for electrochemical oxidation and the sample loading tip for spray ionization. After loading a droplet of the analyte solution onto the tip, two steps were taken to implement quantitation. First, the electrochemical oxidation potential was optimized with cyclic voltammetry followed by coulometric measurements to calculate the amount of oxidized analyte under a constant low voltage within a fixed period of time (5 s). Then, a high voltage (+4.5 kV) was applied to the tip to trigger spray ionization for measuring the oxidation yield from the native analyte ion and its oxidized product ion intensities by mass spectrometry. The analyte's native concentration is quantified by dividing the oxidized product's concentration (based on Coulomb's law) and the oxidation yield (estimated from mass spectrometry [MS] assuming that the parent and oxidation product have nearly the same ionization efficiencies). The workflow has an advantage in being free of any standard for constructing the quantitation curve. Several model compounds (tyrosine, dopamine, and angiotensin II) were selected for method validation. It was demonstrated that this strategy was feasible with an accuracy of ~15% for a wide coverage of different species including endogenous metabolites and peptides. As an example of its possible practical use, it was initially employed to make a bilirubin assay in urine.

First report of pharmaceuticals and personal care products in two tropical rivers of southwestern India

The occurrence of selected pharmaceuticals (trimethoprim, sulfamethoxazole, chloramphenicol, bezafibrate, ceftriaxone, and naproxen) in two west-flowing tropical rivers (Swarna and Nethravati) of southwestern India is reported for the first time. Water samples were collected during the monsoon and post-monsoon seasons from river water end members and further downstream up to their confluence with the adjacent Arabian Sea. Samples were analyzed using HPLC–MS/MS. Results revealed that there were no significant seasonal variations in concentrations of target analytes in both the rivers. Of the total number of samples analyzed (n = 24), trimethoprim was detected in 100% of the samples, whereas sulfamethoxazole (SMX), chloramphenicol (CAP), ceftriaxone (CTX), and naproxen (NPX) were detected in between 91 and 58% of the samples. Bezafibrate (BZF) was not detected in the samples. Nethravathi river showed higher concentrations of pharmaceuticals than the Swarna river which may be attributed to comparatively larger human population in the basin. Possible impacts of PPCPs on aquatic life offer further scope for study.

Kinetic Exclusion Assay of Biomolecules by Aptamer Capture.

DNA aptamers are short nucleotide oligomers selected to bind a target ligand with affinity and specificity rivaling that of antibodies. These remarkable features recommend aptamers as candidates for analytical and therapeutic applications that traditionally use antibodies as biorecognition elements. Numerous traditional and emerging analytical techniques have been proposed and successfully implemented to utilize aptamers for sensing purposes. In this work, we exploited the analytical capabilities offered by the kinetic exclusion assay technology to measure the affinity of fluorescent aptamers for their thrombin target and quantify the concentration of analyte in solution. Standard binding curves constructed by using equilibrated mixtures of aptamers titrated with thrombin were fitted with a 1:1 binding model and provided an effective Kd of the binding in the sub-nanomolar range. However, our experimental results suggest that this simple model does not satisfactorily describe the binding process; therefore, the possibility that the aptamer is composed of a mixture of two or more distinct Kd populations is discussed. The same standard curves, together with a four-parameter logistic equation, were used to determine “unknown” concentrations of thrombin in mock samples. The ability to identify and characterize complex binding stoichiometry, together with the determination of target analyte concentrations in the pM–nM range, supports the adoption of this technology for kinetics, equilibrium, and analytical purposes by employing aptamers as biorecognition elements.

Deep learning-enabled point-of-care sensing using multiplexed paper-based sensors

We present a deep learning-based framework to design and quantify point-of-care sensors. As a use-case, we demonstrated a low-cost and rapid paper-based vertical flow assay (VFA) for high sensitivity C-Reactive Protein (hsCRP) testing, commonly used for assessing risk of cardio-vascular disease (CVD). A machine learning-based framework was developed to (1) determine an optimal configuration of immunoreaction spots and conditions, spatially-multiplexed on a sensing membrane, and (2) to accurately infer target analyte concentration. Using a custom-designed handheld VFA reader, a clinical study with 85 human samples showed a competitive coefficient-of-variation of 11.2% and linearity of R2 = 0.95 among blindly-tested VFAs in the hsCRP range (i.e., 0–10 mg/L). We also demonstrated a mitigation of the hook-effect due to the multiplexed immunoreactions on the sensing membrane. This paper-based computational VFA could expand access to CVD testing, and the presented framework can be broadly used to design cost-effective and mobile point-of-care sensors.

Ultrafast laser micro-nano structured superhydrophobic teflon surfaces for enhanced SERS detection via evaporation concentration

Abstract Evaporation concentration of target analytes dissolved in a water droplet based on superhydrophobic surfaces could be able to break the limits for sensitive trace substance detection techniques (e.g. SERS) and it is promising in the fields such as food safety, eco-pollution, and bioscience. In the present study, polytetrafluoroethylene (PTFE) surfaces were processed by femtosecond laser and the corresponding processing parameter combinations were optimised to obtain surfaces with excellent superhydrophobicity. The optimal parameter combination is: laser power: 6.4 W; scanning spacing: 40 μm; scanning number: 1; and scanning path: 90 degree. For trapping and localising droplets, a tiny square area in the middle of the surface remained unprocessed for each sample. The evaporation and concentration processes of droplets on the optimised surfaces were performed and analyzed, respectively. It is shown that the droplets with targeted solute can successfully collect all solute into the designed trapping areas during evaporation process on our laser fabricated superhydrophobic surface, resulting in detection domains with high solute concentration for SERS characterisation. It is shown that the detected peak intensity of rhodamine 6G with a concentration of 10−6 m in SERS characterisation can be obviously enhanced by one or two orders of magnitude on the laser fabricated surfaces compared with that of the unprocessed blank samples.

Ratiometric Fluorogenic RNA-Based Sensors for Imaging Live-Cell Dynamics of Small Molecules.

Imaging the cellular dynamics of metabolites and signaling molecules is critical for understanding various metabolism and signal transduction pathways. Genetically encoded RNA-based sensors are emerging powerful tools for this purpose. However, it was challenging to use these sensors to precisely determine the intracellular concentrations of target analytes. To solve this problem, we have recently developed ratiometric sensors using an orthogonal pair of RNA/fluorophore conjugates: Broccoli/DFHBI-1T (3,5-difluoro-4-hydroxybenzylidene-1-trifluoroethyl-imidazolinone) and DNB (dinitroaniline-binding aptamer)/SR-DN (sulforhodamine B-dinitroaniline). The cellular DNB-to-Broccoli fluorescence intensity ratio can be directly applied to quantify the target concentrations at the single-cell level. Unfortunately, due to the instability of the SR-DN dye, this ratiometric sensor is difficult to use for monitoring target dynamics. Herein, by replacing SR-DN with a stable TMR (tetramethylrhodamine)-DN dye, we developed a ratiometric sensor system based on Broccoli/DFHBI-1T and DNB/TMR-DN, which can be used for dynamic imaging in living cells. We believe these advanced genetically encoded ratiometric sensors can be widely used for intracellular studies of various target analytes.

Plasmonic biosensors fabricated by galvanic displacement reactions for monitoring biomolecular interactions in real time

Optical sensors are prepared by reduction of gold ions using freshly etched hydride-terminated porous silicon, and their ability to specifically detect binding between protein A/rabbit IgG and asialofetuin/Erythrina cristagalli lectin is studied. The fabrication process is simple, fast, and reproducible, and does not require complicated lab equipment. The resulting nanostructured gold layer on silicon shows an optical response in the visible range based on the excitation of localized surface plasmon resonance. Variations in the refractive index of the surrounding medium result in a color change of the sensor which can be observed by the naked eye. By monitoring the spectral position of the localized surface plasmon resonance using reflectance spectroscopy, a bulk sensitivity of 296 nm ± 3 nm/RIU is determined. Furthermore, selectivity to target analytes is conferred to the sensor through functionalization of its surface with appropriate capture probes. For this purpose, biomolecules are deposited either by physical adsorption or by covalent coupling. Both strategies are successfully tested, i.e., the optical response of the sensor is dependent on the concentration of respective target analyte in the solution facilitating the determination of equilibrium dissociation constants for protein A/rabbit IgG as well as asialofetuin/Erythrina cristagalli lectin which are in accordance with reported values in literature. These results demonstrate the potential of the developed optical sensor for cost-efficient biosensor applications.Graphical abstract

P109 PASSIVE ECCRINE SWEAT SENSING FOR DUPLEX TEMPORAL DETECTION OF CYTOKINES

Abstract Introduction Sweat based wearable sensors have shown a lot of promise in the recent years due to the ability of tracking the biomarkers in real-time. Among the various biomarkers present in sweat, cytokine concentrations have been shown in comparable range to the blood cytokines. Detection of sweat cytokines can help in monitoring of inflammation in real-time. In this work, we demonstrate a duplex cytokine sweat based sensor for real-time monitoring. The developed sensor can detect interleukin-6 (IL-6) and interleukin-10 (IL-10) in real-time that can aid in prognosis or recovery of inflammation. Materials and Methods The sweat based sensor was developed with semiconducting electrode on porous polymeric substrate on a porous polymer substrate. Affinity capture probes were immobilized on the sensor surface via a thiol-cross linking chemistry. ATR-IR was used to validate immobilization of the capture probes. Electrochemical impedance measurements technique was used to detect the interaction between the specific antibody and target analyte. The impedance response based on the binding interaction was used to quantify the sensor metrics. Results In this work, a sweat sensor platform for the duplex detection of IL-6 and IL-10 has been demonstrated. The conjugation of the antibodies to the sensor surface was confirmed using ATR-IR spectroscopy. Impedance response was used to characterize the sensor performance metrics. Calibration dose response curve was developed with decreasing impedance response for increasing concentrations of target analyte. A limit of detection of 2 pg/mL was obtained with a dynamic range from 2 pg/mL- 200 pg/mL for IL-6. IL-10 demonstrated a limit of detection of 1.5pg/mL with a dynamic range from 1.5- 150pg/mL. The developed sensor demonstrated minimal or no cross-reactivity to non-specific molecules. Conclusion A novel sweat-based biosensor for duplex detection of cytokine markers has been demonstrated. The developed biosensor can detect pro and anti-inflammatory cytokines that can aid in the prognosis or recovery of inflammation.

ZIF-8 silencing shell removed by complexation competition reaction for ultrasensitive electrochemical immunoassay

Aiming to develop a stable and simple immunosensor with superior performance, we designed a new strategy based on complexation competition reaction among CaCO3, zeolitic imidazolate framework (ZIF)-8 and ethylenediamine tetraacetic acid disodium (EDTA) for electrochemical detection of cytokeratin 19 fragment 21-1 (CYFRA21-1). First, immunocomplex was formed by CaCO3-Au modified with antibody, MBs modified with antibody and antigen in tube. Then, excess EDTA was added for complexation reaction with CaCO3 and supernatant containing EDTA without complexation reaction was obtained. Second, Ag nanoparticles (NPs) as signal substance were electrodeposited on the electrode surface, and silenced by ZIF-8 layer generated in situ. The remained EDTA in supernatant was transferred to electrode for etching ZIF-8. The signal of Ag NPs was reactivated, owning to partly removing silencing layer of ZIF-8. Therefore, the concentration of target analyte was quantitatively detected by measuring the current signal of Ag/AgCl. Under optimal conditions, the electrochemical immunosensor had an ultralow detection limit of 3.175 fg mL−1 for CYFRA21-1, with a wide detection range from 10 fg mL−1 to 1 μg mL−1. This work successfully constructed an immunosensor based on complexation competition reaction, which providing a potential route for clinical analysis.

A multi-parameter in-situ water quality analyzer based on a portable document scanner and 3D printed self-sampling cells

This research introduced a new low-cost and multi-parameter analyzer for in-situ measurements of typical nutrients in water bodies. The analyzer consisted of color detection and chromogenic reaction modules. The self-sampling action of the 3D printed sampling/reaction cells was achieved with the cooperative application of rubber bands and dissolvable thread. The target analytes in the collected water sample reacted with the chromogenic reagents that were diffused from the pre-placed glass wool in the cell, producing color compounds. A portable document scanner was employed as a multi-parameter in-situ detector to record the image of the colored solutions in all five cells simultaneously. Based on the image, the corrected grayscale values were derived for target analyte quantitation.The relationships between grayscale values and concentrations of target analytes were established, and the temperature effects were studied. In addition, the practicability of the analyzer was demonstrated by in-situ experiments carried out in four different sites, including a creek, a river dock, a reservoir and a secondary settling tank in a wastewater treatment facility. The results indicated that the analyzer could be used for in-situ measuring of nutrients at μmol/L levels in the water. The nutrient concentrations obtained with the analyzer were comparable with those obtained with the standard methods. The presented analyzer provided new complementary ideas and methods for in-situ rapid measurement of nutrients and other target analytes in various water systems.