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The small molecule aldehydes are volatile organic compounds (VOCs), possessing cytotoxicity and carcinogenicity. Long-term exposure can pose a serious threat to human health. Based on an in-situ reduction colorimetric method to generate silver nanoparticles and induce colorimetric response, we proposed a silver-loaded paper-based colorimetric sensor array for visually detecting and differentiating five relatively common trace small molecule aldehyde gases. The silver ions are immobilized onto a porous filter paper and stabilized by complexing agents of branched polyethyleneimine, ethylenediamine, and 1,6-diaminohexane, respectively. The as-fabricated sensor array expresses remarkable stability and capacity to resist humidity. The qualitative analysis reveals that the sensor array has excellent selectivity for aldehyde gases and displays remarkable anti-interference ability. The quantitative analysis indicates that the sensor array exhibits superior sensitivity for five aldehyde gases, with limits of detection (LODs) of 9.0 ppb for formaldehyde (FA), 3.1 ppm for acetaldehyde (AA), 3.5 ppm for propionaldehyde (PA), 23.8 ppb for glutaric dialdehyde (GD), and 71.5 ppb for hydroxy formaldehyde (HF), respectively. Importantly, these LODs are all comfortably below their respective permissible exposure limits. A unique colorimetric response fingerprint is observed for each analyte. Standard chemometric methods illustrate that the sensor array has excellent clustering capability for these aldehyde gases. Additionally, the sensor array's response is irreversible and possesses outstanding performance for cumulative monitoring. This colorimetric sensor array based on silver ions reduced to silver nanoparticles offers a novel detection method for the continuous, ultrasensitive, and visual detection of trace airborne pollutants. [Display omitted] • A paper-based colorimetric sensing platform by using silver ions for the visual detection was constructed. • The sensor array can effectively differentiate and identify five small molecule aldehyde gases. • With the protection from complexing agents, silver ions own high stability and detection activity on paper bases. • Porous structure of filter paper is beneficial for the silver ions enrichment and gases adsorption. [ABSTRACT FROM AUTHOR]

Abstract In this study, a method for direct screening and identification of α-glucosidase inhibitors (AGIs) from extracts of natural products was established based on polyamidoamine (PAMAM) coated magnetic microspheres. A facile route to synthesize the magnetic PAMAM was employed and α-glucosidase was successfully covalently attached to its surface through cross linking of glutaraldehyde. Using the enzyme-loaded magnetic microspheres, potential inhibitors were fished out from crude extracts directly, followed by structure confirmation. The inhibitory activities of the screened components were further investigated by the enzyme-loaded magnetic microspheres. The Fe 3 O 4 @PAMAM@α-Glu microspheres displayed favorable dispersibility, fast magnetic separation, large enzyme binding amount (42.9 μg•mg−1) and high enzyme activity. Moreover, the α-glucosidase on the surface of PAMAM coating maintained high storage stability and remarkable reusability. Taking advantage of specific interaction of the α-glucosidase with AGIs, the materials could selectively capture a known AGI (+)-catechin under the interference of an inactive compound salicylic acid, with a binding capacity as high as 15.4%. Additionally, using the Fe 3 O 4 @PAMAM@α-Glu microspheres in the inhibition assay, the enzymatic reaction could be stopped by magnetic separation instead of the traditional addition of Na 2 CO 3 solution, which not only eliminated the disturbance of termination reagent to the results, but also reused the immobilized α-glucosidase. The screening and inhibitory activity verification of potential ligands in Radix Paeoniae Rubra ("Chi-shao" in Chinese) extracts were achieved by using Fe 3 O 4 @PAMAM@α-Glu microspheres, demonstrating practical applicability of our method. Therefore, the magnetic PAMAM-based screening approach could be a feasible and alternative strategy for discovering enzyme inhibitors from natural product extracts. Graphical abstract fx1 Highlights • Synthesized PAMAM coated magnetic microspheres for α-glucosidase immobilization. • Presents a new approach to directly fish out potential inhibitors from crude extracts. • Inhibitory activities assay of the screened components by the enzyme-loaded magnetic microspheres. • Screening and inhibitory activity verification of potential ligands in Radix Paeoniae Rubra extracts. • Feasible and alternative strategy for discovering enzyme inhibitors from natural product extracts. [ABSTRACT FROM AUTHOR]

Abstract An extremely sensitive enzyme sensor for detection of 17β-estradiol based on electropolymerized L -lysine molecules on a glassy carbon electrode (GCE) modified with critic acid@graphene (CA-GR) and cross-linked with laccase enzyme has been developed in this work. As the laccase immobilization, glutaraldehyde was chosen as cross-linker through the groups reactions. The novel enzyme sensor could recognize and determinate 17β-estradiol effectively. The morphology of the enzyme modified electrode was characterized by transmission electron microscopy (TEM) and electron microscopy (SEM). The amino interaction between cross-linker and enzyme was characterized by Fourier transform infrared spectroscopy (FTIR). Under the optimal experimental conditions, good linear relationships were achieved in the range of 4 × 10–13 − 5.7 × 10–11 M and a limit of detection as low as 1.3 × 10–13 M. Moreover, the enzyme sensor exhibited good reproducibility, stability and high selectivity to 17β-estradiol. Excellent performance was showed in the human urine samples analysis, thus confirming great prospect for further application in clinic diagnosis and biological research. Graphical abstract 1. The preparation of the Lac/Poly L -lysine/CA-GR/GCE 2. The electrocatalytic mechanism proposed for the enzyme biosensor. fx1 Highlights • A enzyme biosensor was developed for ultra-trace 17β-estradiol detection based on Lac/PLLY/CA-GR/GCE. • The bio-film Poly L-lysine coated laccase enzyme molecules that generated stable three-dimensional structure and attracted more mediator to catalyze the oxidation of estradiol. • The Poly L-lysine films were used to achieve better conductivity and linking with laccase enzyme more solid than self-assembly monolayers. • L-lysine, amino acids, also can be served as a matrix for developing other enzyme sensors. [ABSTRACT FROM AUTHOR]

A common drawback of silica-based polar stationary phase is obvious bleeding, probably resulting from silica dissolution in water attracted onto silica gel. Recently we have reported a polyvinyl alcohol (PVA) encapsulated silica gel stationary phase for hydrophilic interaction liquid chromatography (HILIC), which demonstrated good chromatographic performance. Although PVA coating outside could shield SiO 2 inside from erosion by aqueous solution to a certain degree, obvious bleeding of such phase was still observed. To eliminate or reduce the bleeding level of the phase, fabricating multi-layers of PVA coating crosslinked with glutaraldehyde onto silica gel is performed (PVA-GA-Sil). ∼20-fold decrease of the bleeding for PVA-GA-Sil can be achieved relative to bare silica gel, which is much lower than (or comparable to) commercial HILIC phases. PVA-GA-Sil also showed chromatographic performance and demonstrated superiority to commercial columns operated at gradient mode. [ABSTRACT FROM AUTHOR]

Previous studies have confirmed that cytokeratin 19 fragment antigen 21-1 (CYFRA 21-1) serves as a powerful biomarker in non-small cell lung cancer (NSCLC). Herein, we report for the first time a label-free electrochemical immunosensor for sensitive and selective detection of tumor marker CYFRA21-1. In this work, three-dimensional graphene @ gold nanoparticles (3D-G@Au) nanocomposite was modified on the glassy carbon electrode (GCE) surface to enhance the conductivity of immunosensor. The anti-CYFRA21-1 captured and fixed on the modified GCE through the cross-linking of chitosan (CS), glutaraldehyde (GA) and anti-CYFRA21-1. The differential pulse voltammetry (DPV) peak current change due to the specific interaction between anti-CYFRA21-1 and CYFRA21-1 on the modified electrode surface was utilized to detect CYFRA21-1. Under optimized conditions, the proposed electrochemical immunosensor was employed to detect CYFRA21-1 and exhibited a wide linear range of 0.25–800 ng mL −1 and low detection limit of 100 pg mL −1 (S/N = 3). Moreover, the recovery rates of serum samples were in the range from 95.2% to 108.7% and the developed immunosensor also shows a good correlation (less than 6.6%) with enzyme-linked immunosorbent assay (ELISA) in the detection of clinical serum samples. Therefore, it is expected that the proposed immunosensor based on a 3D-G@Au has great potential in clinical medical diagnosis of CYFRA21-1. [ABSTRACT FROM AUTHOR]

A reagent-less amperometric glucose biosensor operating in not-stirred sample solution was developed. A working electrode of the designed biosensor was based on a graphite rod (GR) electrode, which was modified with 1,10-phenanthroline-5,6-dione (PD) and glucose oxidase (GOx). The PD and the GOx were layer-by-layer adsorbed on the GR electrode surface with subsequent drying followed by chemical cross-linking of the adsorbed GOx with glutaraldehyde (GA). Optimal preparation conditions of the working electrode (GR/PD/GOx) were achieved with 12.6 μg and 0.24 mg loading amount of PD and GOx, respectively and 25 min lasting cross-linking of the GOx with GA. A current response to glucose of the GR/PD/GOx electrode was measured at +200 mV potential vs Ag/AgCl reference electrode. Maximum current response was registered when the pH of the buffer solution was 6.0. The registered current response to glucose was linear in the concentration range of 0.1–76 mmol L –1 (R 2 =0.9985) and a detection limit was 0.025 mmol L –1 . The GR/PD/GOx electrode demonstrated good reproducibility and repeatability with the relative standard deviation of 6.2% and 1.8% (at 4.0 mmol L –1 of glucose), respectively, high anti-interference ability to uric and ascorbic acids. It was highly selective to glucose and demonstrated good accuracy in the analysis of human serum samples. [ABSTRACT FROM AUTHOR]

We have constructed biobarcode labels based on 468 nm diameter latex spheres. Modification with polyallylamine and then glutaraldehyde was used to attach a high DNA loading, consisting of aminated probe DNA (approx. 1.01×10 2 molecules per sphere) and biobarcode DNA (approx. 1.66×10 4 molecules per sphere). Detection of the biobarcodes was performed by application of a Ag enhancer solution, causing association of the Ag + ions with the phosphate groups of the DNA. The deposited Ag was detected by differential pulse voltammetry. A 30 mer sequence from the BL21 strain of E. coli was detected with an LOD of 2.6 fM (calibration range 10 aM to 0.1 pM, r 2 =0.91, n =45). The LOD was lowered to 0.56 aM (calibration range 100 zM to 0.1 nM, r 2 =0.991, n =50) by utilizing a sandwich assay with PNA-modified screen printed electrodes, which lowered the Ag background current. The sandwich assay platform was used to calibrate E. coli strain BL2(DE3) with an LOD of 17.0 CFU mL −1 (calibration range 10 to 10 6 CFU mL −1 , r 2 =0.99, n =33) with good discrimination against Salmonella . [ABSTRACT FROM AUTHOR]

A sensitive and facile molecular imprinted sensor has been fabricated using edge plane pyrolytic graphite (EPPG) for the determination of an important oxidative DNA damage product, 8-hydroxydeoxyguanosine (8-OHdG). The molecularly imprinted polymer film was fabricated by electropolymerization of melamine in the presence of 8-OHdG, on glutaraldehyde/poly 1,5-diaminonaphthalene modified EPPG. The imprinted sensor surface was characterized by using Field Emission Scanning Electron Microscopy, Electron Impedance Spectroscopy, Cyclic Voltammetry, Square Wave Voltammetry and UV–visible spectroscopy. The calibration response was linear over a concentration range of 20×10 −9 –3×10 −6 M of 8-OHdG with sensitivity and limit of detection (3σ/b) as 10.59 µM/µA and 3×10 −9 M respectively. The common metabolites in urine, like uric acid, ascorbic acid, xanthine, hypoxanthine do not interfere up to 100-fold concentration. The imprinted sensor is also successfully employed for the determination of 8-OHdG in human urine sample of a renal failure patient. [ABSTRACT FROM AUTHOR]

The use of enzymes immobilized on magnetic nanoparticles to detect contaminants in aqueous samples has gained interest, since it allows the magnetic control, concentration and reuse of the enzymes. In this work, the detection of trace amounts of organophosphate pesticides (chlorpyrifos) and antibiotics (penicillin G) in water was attained by developing a nanoassembly formed by either inorganic or biomimetic magnetic nanoparticles used as substrates to immobilize acetylcholinesterase (AChE) and β-lactamase (BL). Other than the substrate, the optimization of the nanoassembly was done by testing enzyme immobilization both through electrostatic interaction (also reinforced with glutaraldehyde) and covalent bonds (by carbodiimide chemistry). Temperature (25 °C), ionic strength (150 mM NaCl) and pH (7) were set to ensure enzymatic stability and to allow both the nanoparticles and the enzymes to present ionic charges that would allow electrostatic interaction. Under these conditions, the enzyme load on the nanoparticles was ⁓0.1 mg enzyme per mg nanoparticles, and the preserved activity after immobilization was 50–60% of the specific activity of the free enzyme, being covalent bonding the one which yielded better results. Covalent nanoassemblies could detect trace concentrations of pollutants down to 1.43 nM chlorpyrifos and 0.28 nM penicillin G. They even permitted the quantification of 14.3 μM chlorpyrifos and 2.8 μM penicillin G. Also, immobilization conferred higher stability to AChE (⁓94% activity after 20 days storage at 4 °C) and allowed to reuse the BL up to 12 cycles. [Display omitted] • Acetylcholinesterase (AChE) and β-lactamase (BL) can be immobilized on biomimetic magnetic nanoparticles (BMNPs). • Such an immobilization increases enzyme stability and enables their magnetic concentration and reutilization. • AChE-BMNPs and BL-BMNP nanoassemblies can detect 1.43 nM chlorpyrifos and 0.28 nM penicillin G, respectively. [ABSTRACT FROM AUTHOR]

Well-distributed hollow gold nanospheres (Aushell@GOD) (20±5 nm) were synthesized using the glucose oxidase (GOD) cross-linked with glutaraldehyde as a template. A glucose biosensor was prepared based on Aushell@GOD nanospheres for catalyzing luminol electrogenerated chemiluminescence (ECL). Firstly, chitosan was modified in a glassy carbon electrode which offered an interface of abundant amino-groups to assemble Aushell@GOD nanospheres. Then, glucose oxidase was adsorbed on the surface of Aushell@GOD nanospheres via binding interactions between Aushell and amino groups of GOD to construct a glucose biosensor. The Aushell@GOD nanospheres were investigated with TEM and UV-vis. The ECL behaviors of the biosensor were also investigated. Results showed that, the obtained Aushell@GOD nanospheres exhibited excellent catalytic effect towards the ECL of luminol-H2O2 system. The response of the prepared biosensor to glucose was linear with the glucose concentration in the range of 1.0 μM to 4.3 mM (R=0.9923) with a detection limit of 0.3 μM (signal to noise=3). This ECL biosensor exhibited short response time and excellent stability for glucose. At the same time the prepared ECL biosensor showed good reproducibility, sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

Abstract: In this work a novel biosensor for arginine determination based on the urease inhibition effect has been proposed. Ion-selective field effect transistors were used as transducers. Urease immobilized in glutaraldehyde vapor served as a biorecognition element of the biosensor. Significant part of the work was aimed at proving the urease inhibition by arginine. Optimal concentration of urea for arginine determination was chosen. Detection limit for arginine was 0.05mM. The biosensor selectivity towards different amino acids was studied. The results of quantitative determination of l-arginine in the real sample (a drinkable solution “Arginine Veyron”) were in good agreement with the producer's data (a relative error was 5.2%). The biosensor showed a good reproducibility of arginine determination. [Copyright &y& Elsevier]

Abstract: We present a new cysteamine (CS)-modified polyaniline (PANI) film for highly efficient immobilization of biomolecules in biosensing technology. This electrochemical deposited PANI film treated with CS and glutaraldehyde could be employed as an excellent substrate for biomolecules immobilization. The parameters of PANI growth were optimized to obtain suitable surface morphology of films for biomolecules combination with the help of electron and atomic force microscopy. Cyclic voltammetry (CV) was utilized to illustrate the different electrochemical activities of each modified electrode. Due to the existence of sulfydryl group and amino group in CS, surface modification with CS was proven to reduce oxidized units on PANI film remarkably, as evidenced by both ATR-FTIR and Raman spectroscopy characterizations. Furthermore, bovine serum albumin (BSA) was used as the model protein to investigate the immobilization efficiency of biomolecules on the PANI film, comparative study using quartz crystal microbalance (QCM) showed that BSA immobilized on CS-modified PANI could be increased by at least 20% than that without CS-modified PANI in BSA solution with the concentration of 0.1–1mg/mL. The CS-modified PANI film would be significant for the immobilization and detection of biomolecules and especially promising in the application of immunosensor for ultrasensitive detection. [Copyright &y& Elsevier]

Abstract: Piezoelectric immunosensors on the basis of homologous and group-specificantibodies have been developed for detecting penicillin G, ampicillin, and the total content of penicillin antibiotics. The receptor coating of the sensor was obtained by the immobilization of penicillin G or ampicillin hapten–protein conjugates on the polypyrrole film obtained by electropolymerization and activated by glutaraldehyde. The affinity constants and the cross reactivity coefficients have been calculated. This made it possible to estimate the affinity and specificity of the polyclonal and monoclonal antibodies used. The calibration curves are linear in the range of concentrations 2.5–250.0ngml−1 (penicillin G), 2.5–500.0ngml−1 (ampicillin), and 1–500ngml−1 (group of penicillin). The limits of detection are 0.8ngml−1, 3.9ngml−1, which are lower than MRL, established for penicillin antibiotics. The sensors were tested in detecting penicillins in milk, pork, beef, liver. [Copyright &y& Elsevier]

Abstract: Electrochemical impedance immunosensor, with its high sensitivity from electrochemical impedance analysis and ideal specificity from the immunoassay, is increasingly used in the detection of a kind of phenoxy acid herbicides which is 2,4-Dichlorophenoxybutyric acid (2,4-DB). In this experiment, synthetic 2,4-DB antibodies were immobilized on the electrode by the crosslinking of l-Cysteine/glutaraldehyde, and 2,4-DB were measured by the increase of electron-transfer resistance when the immune reaction occurred, with Fe(CN)6 3−/Fe(CN)6 4− as the probe. Under optimal conditions, the change of resistance is in a linear relationship with the logarithm of the concentration in the range of 1.0×10−7–1.0×10−3 g/L (R=0.994) with the detection limit of 1.0×10−7 g/L (0.1ppb). This method bears such merits as simplicity in operation, high sensitivity, wide linear range, specificity, reproducibility and good stability. The actual soybean samples were analyzed with the recovery of 82.8%–102.3%. [Copyright &y& Elsevier]

Abstract: A highly sensitive conductometric biosensor for l-arginine determination was developed by exploiting the unique biorecognition capacities of two enzymes of urea cycle – arginase (E.C. 3.5.3.1) and urease (E.C. 3.5.1.5). The enzymes were co-immobilized in a single bioselective membrane on the working sensor, while a lysine rich bovine serum albumin (BSA) membrane was immobilized on the reference sensor, allowing differential measurements. The optimum percentage ratio of arginase and urease within the bioselective membrane was determined when the biosensor sensitivity to l-arginine and urea was optimum. Analytical characteristics of the conductometric biosensor for l-arginine determination were compared for two types of enzyme immobilization (cross-linking with glutaraldehyde (GA) and entrapment in the polymeric membrane). The optimum features in terms of the sensitivity, the linear range, and the detection limit (4.2μS/mM, 0.01–4mM, and 5.0×10−7 M, respectively) were found for l-arginine biosensor based on enzyme cross-linking with GA. A quantitative determination of l-arginine in the real sample (a drinkable solution “Arginine Veyron”) gave a satisfactory result compared to the data provided by the producer (a relative error was 4.6%). The developed biosensor showed high operational and storage stability. [Copyright &y& Elsevier]

Abstract: A simple and sensitive method for amplified chemiluminescent immunoassay has been developed by using multiple signal antibodies functionalized titania nanoparticle as tracer. This nanocomposite was fabricated by sequentially conjugating bovine serum albumin and horseradish peroxidase-labeled antibody onto the surface of titania nanoparticles using glutaraldehyde as the linkage. After a sandwich immuno-binding process, the captured nanocomposite tracer greatly catalyzed the luminol chemiluminescence reaction to produce a strong signal. Human IgG was detected as a model analyte, and a linear range of 0.5–200ngmL−1 was obtained. The detection limit of the proposed method was 0.1ngmL−1, which was 50-folds lower than that using the traditional tracer. The reproducibility, the stability and the specificity of the proposed immunoassay method were acceptable. The results for real sample analysis also demonstrated its application potential in some important areas such as clinical diagnosis. [Copyright &y& Elsevier]

Abstract: In this paper, we represent a label-free biosensor based on immobilization of serum antibodies for rapid detection of viral antigens. Human serum containing specific antibodies against Japanese encephalitis virus (JEV) was immobilized on a silanized surface of an interdigitated sensor via protein A/glutaraldehyde for electrical detection of JEV antigens. The effective immobilization of serum antibodies on the sensor surface was verified by Fourier transform infrared spectrometry and fluorescence microscopy. The signal of the biosensor obtained by the differential voltage converted from the change into non-Faradic impedance resulting from the specific binding of JEV antigens on the surface of the sensor. The detection analyzed indicates that the detection range of this biosensor is 1–10μg/ml JEV antigens, with a detection limit of 0.75μg/ml and that stable signals are measured in about 20min. This study presents a useful biosensor with a high selectivity for rapid and simple detection of JEV antigens, and it also proposes the biosensor as a future diagnostic tool for rapid and direct detection of viral antigens in clinical samples for preliminary pathogenic screenings in the case of possible outbreaks. [Copyright &y& Elsevier]

Abstract: The current work describes the elaboration of a simple, sensitive and reliable β-casein modified glass beads, for the detection and quantification of its specific antibody anti β-casein. This is an elementary receptor without electronic part, developed by grafting glass bead surface with the antigenic β-casein via 3-aminopropyltriethoxy silane and then glutaraldehyde as cross-linker. The whole is realized by a classical process, called in two steps and in mild conditions where chemical protocol is optimized for β-casein use. The detection and quantification of the specific reaction antibody–receptor is carried out by the technique of the second antibody labeled with horse radish peroxidase (HRP). Our receptor can detect the β-casein antibody present in the serum at dilutions up to a factor 107 in strong ionic strength medium. The same antibody of the same serum and in the same conditions can be detected by ELISA test at dilutions up to a factor 105. The whole test, after our receptor realization, takes about 5h. [Copyright &y& Elsevier]

Abstract: The immobilization of tyrosinase onto glutaraldehyde activated streptavidine magnetic particles and subsequent retention onto a magnetized carbon paste electrode for the amperometric assay of tyrosinase inhibitors is described. Tyrosine was used as substrate as it is the first substrate in the melanogenesis process. The sensing mode is based on monitoring the decrease of the amperometric signal corresponding to the electrochemical reduction of dopaquinone enzymatically generated. This current decrease is due to the presence of inhibitors acting directly on the enzyme or inhibitors acting on the product of the enzymatic reaction, i.e. dopaquinone. The methodology is designed for the evaluation of the inhibitory potency of the most frequently used active substances in cosmetic marketed products against hyperpigmentation such as kojic acid, azelaic acid and benzoic acid. These compounds bind to the tyrosinase active center. Ascorbic acid is also investigated as it interrupts the synthesis pathway of melanin by reducing the melanin intermediate dopaquinone back to l-dopa. By comparing the obtained IC50, under the same experimental conditions, the order of their inhibitory potency was: kojic acid (IC50 =3.7×10−6 M, K i =8.6×10−7 M), ascorbic acid (IC50 =1.2×10−5 M), benzoic acid (IC50 =7.2×10−5 M, K i =2.0×10−5 M) and azelaic acid (IC50 =1.3×10−4 M, K i =4.2×10−5 M) in close agreement with literature spectrophotometric inhibition data using the soluble tyrosinase. [ABSTRACT FROM AUTHOR]

Abstract: A poly(vinyl alcohol) film cross-linked with glutaraldehyde (PVA–GA) was introduced to the surface of a tyrosinase-based carbon paste electrode. The coated PVA–GA film was beneficial in terms of increasing the stability and reproducibility of the enzyme electrode. The electrode showed a sensitive current response to the reduction of the o-quinone, which was the oxidation product of phenol, by the tyrosinase, in the presence of oxygen. The effects of the PVA and PVA–GA coating, the pH, and the GA:PVA ratio on the current response were investigated. The sensitivity of the PVA–GA–Tyr electrode was 130.56μA/mM (1.8μA/μMcm2) and the linear range of phenol was 0.5–100μM. At a higher concentration of phenol (>100μM), the current response showed the Michaelis–Menten behavior. Using the PVA–GA–Tyr electrode, a two-electrode system was tested as a prototype sensor for portable applications. [Copyright &y& Elsevier]

Hydrogels are 3D polymeric networks with great swelling capability in water and appropriate chemical, mechanical and biological features which make it feasible to maintain bioactive substances. Herein, we fabricated carbon dots-chitosan nanocomposite hydrogels via reacting carbon dots synthesized from various aldehyde precursors with chitosan after that functionalized with ssDNA probe for detection of microRNA-21 in MCF-7 cancer cells. More importantly, three fluorescent hydrogels were produced using schiff base reaction (forming imine bonds) among the amine in chitosan and aldehyde groups on the CDs surface. Furthermore, the hydrogel films, CDs and CDs-chitosan nanocomposite hydrogels were characterized by UV–vis absorption and fluorescence spectra, FT-IR, scanning electron microscope (SEM) and transmission electron microscopy (TEM). The DNA hydrogel bioassay strategy revealed a great stability and a superb sensitivity for microRNA-21, with a suitable linear range (0.1–125 fM) and a detection limit (0.03 fM). For sample analysis, the biosensors exhibited good linearity with MCF-7 cancer cell concentrations from 1000 to 25000, 1000–25000 and 1000–6000 cells mL−1 and detection limit of 310, 364 and 552 cells mL−1, for glutaraldehyde, nitrobezaldehyde and benzaldehyde based nanocomposite hydrogels, respectively. In addition, cell viability consequences demonstrated low probe cytotoxicity, so nanocomposite hydrogels was utilized to multicolor imaging of MCF-7 cancer cells. Image 1 • A 3D hydrogel based on carbon dots and chitosan fabricated for sensitive quantification of micRNA-21 in MCF-7 cancer cells. • The proposed assay applied for detection of micRNA-21 in concentration range of 0.1-125 fM with detection limit of 0.03 fM. • Fluorescent hydrogels produced using schiff base reaction among the amine groups in chitosan and aldehyde groups of CDs. • The quenching of the fluorescence intensity of CDs-CH nanocomposite hydrogels can be due to the aggregation of CDs. [ABSTRACT FROM AUTHOR]

A novel sensitive electrochemical immunosensor has been designed for determination of tacrolimus (Tac) based on spherical carrier amplification strategy. In this work, a spherical signal carrier was prepared by conjugating gold nanorods (AuNRs) functionalized L-cysteine (AuNRs@L-Cys) onto polystyrene nanoparticles (PS) to form a nanostructure, greatly increasing the amount of loaded capture antibodies. The PS was a stable spherical functional polymer with large specific surface area and was labeled with AuNRs@L-Cys via coupling reagent to increase active groups, biocompatibility and conductivity. The capture antibodies could be attached on the PS- AuNRs@L-Cys via linkage reagent glutaraldehyde (GA). Furthermore, single-layer molybdenum disulfide (MoS 2) fixed by chitosan were utilized to construct the base of this immunosensor, increasing the carrying capacity and stability of the electrode. After electrochemical reduction, the conductivity and electron transfer rate of MoS 2 were obviously improved, which offered a platform for this immunosensor and further amplified the signal. Under the optimized conditions, the proposed immunosensor revealed a linear Tac-concentration behavior from 1.0 to 30 ng mL−1 with a detection limit of 0.17 ng mL−1 (S/N = 3). The immunoassay was successfully applied to the quantification of Tac in serum samples with acceptable precision. The results indicated that a potentially analytical platform may be used to recognize the concentration of other drugs. Image 1 • A spherical signal carrier was constructed to form a brush structure and to achieve the amplification strategy. • The electrochemical reduction of MoS 2 was carried out to improve conductivity and electron transfer rate of electrode. • A novel method that combined immune response with electrochemistry for the detection of tacrolimus was developed. • Compared with others methods, the detection limit and linear range of this method are ideal. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR) biosensors are often used in the detection of solid, liquid or gaseous samples in diagnostics, pharmaceutics and military defense. Plasmon waveguide resonance (PWR) mode is obtained when a dielectric waveguide layer is added to the metal film. In this study, a self-referenced PWR (SRPWR) silicon dioxide (SiO 2) chip was examined. The self-referenced measurement is important to compensate for temperature fluctuations, other instabilities and allows RI signal measurement without an additional reference sample, thus minimising the sample volume needed. The chip was fabricated with a multi-layer of metals and dielectrics, consisting of a 420 nm SiO 2 layer, a 40 nm Ag layer and another 480 nm SiO 2 layer. This chip was shown to give one internal plasmon excited on the bottom interface SiO 2 /Ag, which is used as self-reference in the detection. The top layer acts as a waveguide layer and can be designed to give modes with ultrahigh penetration depth. A direct assay was developed, where the recognition molecule (specific antibody) was immobilized onto the SiO 2 plasmonic chip surface, via a covalent coupling protocol based on 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde. The SRPWR biosensor was developed for the sensing of two chosen stroke biomarkers: NT-proBNP and S100β, which are sensitive and specific for stroke diagnostics. For both biomarkers, a linear decreasing pattern in the RI signal was recognized with the increasing biomarkers concentrations. Biomarkers detection was conducted in deionized water and validation was done in spiked porcine plasma. The SiO 2 based plasmonic chip demonstrates a limit-of-detection of less than 1 ng/mL that is clinically relevant for both stroke biomarkers. A self-referenced plasmon-waveguide-resonance (SRPWR) silicon dioxide (SiO 2) chip was developed with the purpose of detecting two chosen stroke biomarkers, n-terminal pro brain natriuretic peptide (NT-proBNP) and S100β, which are sensitive and specific for stroke diagnostics. The self-referenced measurement is important to compensate for temperature fluctuations and other instabilities. This also allows to conduct accurate measurements of the refractive index (RI) signal without the need for an additional reference sample, thus minimising the sample volume needed. For both biomarkers, a linear decreasing pattern in the RI signal was recognized with the increasing biomarkers concentrations. The SiO 2 based plasmonic chip demonstrates a limit-of-detection of less than 1 ng/mL that is clinically relevant for both stroke biomarkers. Image 1 • Self-referenced plasmon waveguide resonance silicon dioxide biosensor was developed. • Sensing of NT-proBNP and S100β as biomarkers for stroke diagnostics. • The self-referenced chip allows signal measurement without reference sample. • Antibody was immobilized on the plasmonic chip surface via covalent coupling. • Linear decreasing pattern was recognized with increasing biomarkers concentrations. [ABSTRACT FROM AUTHOR]

Human Exhaled Breath Condensate (EBC) contains markers of several inflammatory diseases. Its analysis is of interest to a number of researchers. Nitrite ions (NO 2 -), which are widely used in our daily lives, are nevertheless among these indicators. In this study, a simple, fast, portable, non-invasive and cheap electrochemical sensor is developed for the analysis of the nitrite profile in EBC. In this regard, sodium nitrite (NaNO 2) was first immobilized on self-assembled 2-aminothiophenol (2-ATP) on a screen-printed gold electrode (Au-SPE). Then, a polymer matrix composed of polyvinyl alcohol (PVA) crosslinked with glutaraldehyde (GA) was combined with gold nanoparticles (Au-NPs) to cover the modified Au-SPE and complete the fabrication of the Ion Imprinted Polymer (IIP) sensor. The electrochemical behaviour of the sensor was monitored using Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and Differential Pulse Voltammetry (DPV) methods, while the morphology and chemical composition of its layers were observed by infrared Fourier transform (FTIR), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy coupled with energy dispersion X-Ray spectroscopy (SEM-EDS) techniques. In addition, after a successful control test using a Non-Imprinted Ion Polymer (NIIP) sensor, the obtained results demonstrated satisfactory sensitivity and selectivity to nitrite compared to co-existing interfering substances in EBC, such as nitrate, acetate and ammonium nitrate. Under improved experimental conditions, the nitrite IIP sensor exhibits responses proportional to nitrite concentrations (R2 = 0.96) over a concentration range of 0.5–50 μg mL−1 with a detection limit (LOD) of 4 μmol L−1 (signal-to-noise ratio S/N = 3). The proposed approach was well applied for the nitrite determination in EBC samples with a relative standard deviation (RSD = 4%) and could open clinical applications in respiratory medicine. Image 1 • Successful development of an electrochemical nitrite sensor-based ion imprinted polymer. • CV, DPV, EIS, FTIR, AFM and SEM techniques for electrochemical and morphological characterizations. • Utilization of the IIP sensor for nitrite determination in exhaled breath condensate. • A lower LOD of 4 μmol L−1 over a working range from 0.5 to 50 μg mL−1 compared with reported works. [ABSTRACT FROM AUTHOR]