Detection of white spot syndrome virus in seafood samples using a magnetosome-based impedimetric biosensor.

White spot syndrome virus (WSSV) is a significant threat to the aquaculture sector, causing mortality among crabs and shrimps. Currently available diagnostic tests for WSSV are not rapid or cost-effective, and a new detection method is therefore needed. This study demonstrates the development of a biosensor by functionalization of magnetosomes with VP28-specific antibodies to detect WSSV in seafood. The magnetosomes (1 and 2 mg/ml) were conjugated with VP28 antibody (0.025-10 ng/µl), as confirmed by spectroscopy. The magnetosome-antibody conjugate was used to detect the VP28 antigen. The binding of antigen to the magnetosome-antibody complex resulted in a change in absorbance. The magnetosome-antibody-antigen complex was then concentrated and brought near a screen-printed carbon electrode by applying an external magnetic field, and the antigen concentration was determined using impedance measurements. The VP28 antigen (0.025 ng/µl) bound more efficiently to the magnetosome-VP28 antibody complex (0.025 ng/µl) than to the VP28 antibody (0.1 ng/µl) alone. The same assay was repeated to detect the VP28 antigen (0.01 ng/µl) in WSSV-infected seafood samples using the magnetosome-VP28 antibody complex (0.025 ng/µl). The WSSV in the seafood sample was also drawn toward the electrode due to the action of magnetosomes controlled by the external magnetic field and detected using impedance measurement. The presence of WSSV in seafood samples was verified by Western blot and RT-PCR. Cross-reactivity assays with other viruses confirmed the specificity of the magnetosome-based biosensor. The results indicate that the use of the magnetosome-based biosensor is a sensitive, specific, and rapid way to detect WSSV in seafood samples.

Fully Printed Wearable Microfluidic Devices for High-Throughput Sweat Sampling and Multiplexed Electrochemical Analysis.

Although the recent advancement in wearable biosensors provides continuous, noninvasive assessment of physiologically relevant chemical markers from human sweat, several bottlenecks still exist for its practical use. There were challenges in developing a multiplexed biosensing system with rapid microfluidic sampling and transport properties, as well as its integration with a portable potentiostat for improved interference-free data collection. Here, we introduce a clean-room free fabrication of wearable microfluidic sensors, using a screen-printed carbon master, for the electrochemical monitoring of sweat biomarkers during exercise activities. The sweat sampling is enhanced by introducing low-dimensional sensing compartments and lowering the hydrophilicity of channel layers via facile silane functionalization. The fluidic channel captures sweat at the inlet and directs the real-time sweat through the active sensing electrodes (within 40 s) for subsequent decoding and selective analyses. For proof of concept, simultaneous amperometric lactate and potentiometric ion sensing (Na+, K+, and pH) are carried out by a miniature circuit board capable of cross-talk-free signal collection and wireless signal transduction characteristics. All of the sensors demonstrated appreciable sensitivity, selectivity, stability, carryover efficiency, and repeatability. The floating potentiometric circuits eliminate the signal interference from the adjacent amperometric transducers. The fully integrated pumpless microfluidic device is mounted on the epidermis and employed for multiplexed real-time decoding of sweat during stationary biking. The regional variations in sweat composition are analyzed by human trials at the underarm and upperback locations. The presented method offers a large-scale fabrication of inexpensive high-throughput wearable sensors for personalized point-of-care and athletic applications.

Magnetosome-anti-Salmonella antibody complex based biosensor for the detection of Salmonella typhimurium.

Epidemic Salmonellosis contracted through the consumption of contaminated food substances is a global concern. Thus, simple and effective diagnostic methods are needed. Magnetosome-based biosensors are gaining attention because of their promising features. Here, we developed a biosensor employing a magnetosome-anti-Salmonella antibody complex to detect lipopolysaccharide (somatic "O" antigen) and Salmonella typhimurium in real samples. Magnetosome was extracted from Magnetospirillum sp. RJS1 and characterized by microscopy. The magnetosome samples (1 and 2 mg/mL) were directly conjugated to anti-Salmonella antibody (0.8-200 µg/mL) and confirmed by spectroscopy and zeta potential. The concentrations of magnetosome, antibody and lipopolysaccharide were optimized by ELISA. The 2 mg/mL-0.8 µg/mL magnetosome-antibody complex was optimal for detecting lipopolysaccharide (0.001 µg/mL). Our assay is a cost-effective (60%) and sensitive (50%) method in detection of lipopolysaccharide. The optimized magnetosome-antibody complex was applied to an electrode surface and stabilized using an external magnetic field. Increased resistance confirmed the detection of lipopolysaccharide (at 0.001-0.1 µg/mL) using impedance spectroscopy. Significantly, the R2 value was 0.960. Then, the developed prototype biosensor was applied to food and water samples. ELISA confirmed the presence of lipopolysaccharide in homogenized infected samples and cross reactivity assays confirmed the specificity of the biosensor. Further, the biosensor showed low detection limit (101 CFU/mL) in water and milk sample demonstrating its sensitivity. Regression coefficient of 0.974 in water and 0.982 in milk was obtained. The magnetosome-antibody complex captured 90% of the S. typhimurium in real samples which was also confirmed in FE-SEM. Thus, the developed biosensor is selective, specific, rapid and sensitive for detection of S. typhimurium.

Amperometric determination of Myo-inositol using a glassy carbon electrode modified with nanostructured copper sulfide.

A method for the amperometric determination of Myo-inositol is presented. Nanostructured copper sulfide material was synthesized by solvothermal method and utilized as sensor matrix. The physico-chemical analysis using XRD, Raman, FE-SEM, TEM, and XPS confirmed the formation of CuS material. The voltammetric response of CuS-modified glassy carbon electrode for a successive Myo-inositol (0.5 µM) addition confirmed that the reaction takes place at the surface of the electrode. The modified electrode resulted in signal enhancement for a linear response ranging from 0.5-8.5 µM at an applied overpotential of 0.65 V with a correlation coefficient value (R2) of 0.99. The sensitivity and limit of detection of the modified electrode were 7.87 µA µM-1 cm-2 and 0.24 µM, respectively. The interfering effect of various compounds present in real samples was examined. Graphical abstract Schematic representation of synthetic protocol of nanostructured CuS and Myo-inositol oxidation on CuS-modified glassy carbon electrode in basic medium.

Development of magnetosomes-based biosensor for the detection of Listeria monocytogenes from food sample.

Listeriosis through contaminated food is one of the leading causes of premature deaths in pregnant women and new born babies. Here, the authors have developed a magnetosomes-based biosensor for the rapid, sensitive, specific and cost-effective detection of Listeria monocytogenes from food sample. Magnetosomes were extracted from Magnetospirillum sp. RJS1 and then directly bound to anti-Listeriolysin antibody (0.25-1 µg/ml), confirmed in spectroscopy. Listeriolysin (LLO) protein (0.01-7 µg/ml) was optimised in enzyme-linked immunosorbent assay. Magnetosomes was conjugated with LLO antibody (0.25 µg/ml) in optimum concentration to detect LLO protein (0.01 µg/ml). Magnetosomes-LLO antibody complex was 25% cost effective. The magnetosomes-LLO antibody complex was directly stabilised on screen printed electrode using external magnet. The significant increase in resistance (RCT value) on the electrode surface with increase in concentration of LLO protein was confirmed in impedance spectroscopy. The L. monocytogenes contaminated milk and water sample were processed and extracted LLO protein was detected in the biosensor. The specificity of the biosensor was confirmed in cross-reactivity assay with other food pathogens. The detection limit of 101 Cfu/ml in both water and milk sample manifests the sensitive nature of the biosensor. The capture efficiency and field emission scanning electron microscopy confirmed positive interaction of Listeria cells with magnetosomes-antibody complex.

An electrochemical sensor for homocysteine detection using gold nanoparticle incorporated reduced graphene oxide.

In this work, we report a methodology for the quantification of Homocysteine (HcySH) at neutral pH (pH-7.0) using Au nanoparticles incorporated reduced graphene oxide (AuNP/rGO/GCE) modified glassy carbon electrode. The modified electrode was characterized using SEM and XRD techniques. The electrode exhibited a typical behavior against the standard redox probe [Fe(CN)6]3-/4- and resulted in 0.06 V peak to peak potential value. The modified electrode exhibited electrocatalytic activity towards electrochemical biosensing of HcySH, which is established using voltammetric studies. HcySH oxidation peak potential is observed at 0.12 V on AuNP/rGO/GCE which is 0.7 V cathodic than bare glassy carbon electrode (0.82 V). The large peak potential shift observed is reasoned as the interaction of SH group of HcySH with the gold nanoparticles and the electrocatalytic property of reduced graphene oxide that enhances the electrochemical detection at reduced overpotential. Further, successive addition of HcySH showed a linear increment in the sensitivity within the concentration range of 2-14 mM. From an amperometric protocol, the limit of detection is found as 6.9 µM with a sensitivity of 14.8 nA/µM. From a set of cyclic voltammetric measurements, it is observed that the electrode produces a linear signal on the concentration of HcySH in the presence of hydrogen peroxide. Thus it can be concluded that the matrix can detect HcySH even in the presence of hydrogen peroxide.

A reagentless non-enzymatic hydrogen peroxide sensor presented using electrochemically reduced graphene oxide modified glassy carbon electrode.

Herein, we report a simple, facile and reproducible non-enzymatic hydrogen peroxide (H2O2) sensor using electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode (GCE). The modified electrode was characterized by Fourier transform infrared (FT-IR), UV-Visible, scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. Cyclic voltammetric (CV) analysis revealed that ERGO/GCE exhibited virtuous charge transfer properties for a standard redox systems and showed excellent performance towards electroreduction of H2O2. Amperometric study using ERGO/GCE showed high sensitivity (0.3µA/µM) and faster response upon the addition of H2O2 at an applied potential of -0.25V vs. Ag/AgCl. The detection limit is assessed to be 0.7µM (S/N=3) and the time to reach a stable study state current is <3s for a linear range of H2O2 concentration (1-16µM). In addition, the modified electrode exhibited good reproducibility and long-term stability.

Unusual seedless approach to gold nanoparticle synthesis: application to selective rapid naked eye detection of mercury(II).

We report a novel seedless Hg(2+)-induced synthetic approach for the preparation of gold nanostructures. This protocol is demonstrated for the highly selective and sensitive naked eye detection of Hg(2+) based on the high affinity metallophilic Hg(2+)-Au(+) interaction. The response time upon exposure to Hg(2+) is almost instantaneous.

Synthesis, characterization and antibacterial activity of polyaniline/Pt-Pd nanocomposite.

Pt colloid and Pt-Pd colloid, pristine polyaniline, polyaniline/Pt nanocomposite and polyaniline/Pt-Pd nanocomposite were synthesized by simple chemical method. They were characterized by UV-Vis, FT-IR, XRD, TGA, SEM, HR-SEM and HR-TEM with EDAX techniques. The results proved that there is a strong interaction between metal nanoparticles (Pt-Pd) and polyaniline chains. This interaction creates changes in the backbone chain of polyaniline/Pt-Pd nanocomposite when compared to pristine polyaniline. The synthesized materials were evaluated for antibacterial activity, minimal inhibitory concentration and minimal bactericidal concentration. The results indicated that the nanocomposites exhibited improved antibacterial activity when compared to pristine polyaniline and individual metal colloids. This is the first report on the chemical synthesis of polyaniline/Pt-Pd nanocomposite, which exhibits antibacterial activity at micro molar concentration levels.

Direct electron transfer at a glucose oxidase-chitosan-modified Vulcan carbon paste electrode for electrochemical biosensing of glucose.

This article describes the investigation of direct electron transfer (DET) between glucose oxidase (GOD) and the electrode materials in an enzyme-catalyzed reaction for the development of improved bioelectrocatalytic system. The GOD pedestal electrochemical reaction takes place by means of DET in a tailored Vulcan carbon paste electrode surfaces with GOD and chitosan (CS), allowing efficient electron transfer between the electrode and enzyme. The key understanding of the stability, biocatalytic activity, selectivity, and redox properties of these enzyme-based glucose biosensors is studied without using any reagents, and the properties are characterized using electrochemical techniques like cyclic voltammogram, amperometry, and electrochemical impedance spectroscopy. Furthermore, the interaction between the enzyme and the electrode surface is studied using ultraviolet-visible (UV-Vis) and Fourier transform infrared (FTIR) spectroscopy. The present glucose biosensor exhibited better linearity, limit of detection (LOD = 0.37 ± 0.02 mol/L) and a Michaelis-Menten constant of 0.40 ± 0.01 mol/L. The proposed enzyme electrode exhibited excellent sensitivity, selectivity, reproducibility, and stability. This provides a simple "reagent-less" approach and efficient platform for the direct electrochemistry of GOD and developing novel bioelectrocatalytic systems.

Anodic stripping voltammetric determination of cadmium using a "mercury free" indium film electrode.

In this work, the determination of cadmium has been attempted using an indium film electrode in the presence of bromide ions as an additive, for the first time. The electrode was prepared in situ on a glassy carbon substrate and employed in combination with square wave anodic stripping voltammetry. The purpose of having bromide ions is to enhance the analytical value of cadmium detection. In the absence of bromide ions, cadmium stripping peaks coalesce with indium and it is difficult to resolve for analytical purposes. The addition of bromide ions strongly influences the peak separation, thanks to the complex-forming characteristics of cadmium with bromide ions. Several key operational parameters influencing the electroanalytical response of indium modified electrodes were examined and optimized, such as deposition potential, pH, bromide ion and indium concentration. The indium modified electrode exhibited well-defined, separated stripping signals and revealed good linear behavior in the examined concentration range from 1 to 25 ng ml(-1). The present method shows a low detection limit value of 0.36 ng ml(-1). These results suggest that the proposed electrode contributes to the wider applicability of electrochemical stripping techniques in connection with "mercury-free" electrodes.

Synthesis and characterization of polyaniline/Ag-Pt nanocomposite for improved antibacterial activity.

Polyaniline, polyaniline/Ag-Pt nanocomposite and bimetal (Ag-Pt) colloidal solution were chemically synthesized and characterized by UV-vis, XRD, FT-IR, TGA, HRSEM with EDAX and HRTEM techniques. The results reveal that there was a strong interaction between Ag-Pt nanocomposite and polyaniline chains. This interaction makes only small changes in the backbone chain of polyaniline/Ag-Pt nanocomposite when compared with polyaniline. TGA result revealed greater thermal stability of the composite. HRSEM images showed pebble like morphology for polyaniline/Ag-Pt nanocomposite. The average grain size of Ag-Pt nanoparticle was found to be 2-5 nm, which is confirmed by HRTEM analysis. The polyaniline and polyaniline/Ag-Pt nanocomposite were tested for antibacterial activity. The composite showed improved inhibition efficiency with a maximum zone diameter of 30 ± 1.25 mm against Staphylococcus aureus. This is the first report on the synthesis and its antibacterial activity of polyaniline/Ag-Pt nanocomposite.

Stabilized gold nanoparticles by reduction using 3,4-ethylenedioxythiophene-polystyrenesulfonate in aqueous solutions: nanocomposite formation, stability, and application in catalysis.

Herein, we report a one-pot synthesis of highly stable Au nanoparticles (AuNPs) using 3,4-ethylenedioxythiophene (EDOT) as a reductant and polystyrene sulfonate (PSS-) as a dopant for PEDOT and particle stabilizer. The synthesis demonstrated in this work entails the reduction of HAuCl4 using EDOT in the presence of PSS-. The formation of AuNPs with concomitant EDOT oxidation is followed by UV-vis spectroscopy at various time intervals. Absorption at 525 nm is due to the surface plasmon band of AuNPs (violet), and broad absorption above 700 nm is due to oxidized PEDOT that was further characterized to be in its highly oxidized (doped) state, using FT-Raman spectroscopy. Transmission electron microscopy shows a polydisperse nature of the particles, and the selected area electron diffraction pattern reveals the polycrystalline nature of AuNPs. With stabilizers such as sodium dodecylsulfate (SDS) (green) and polyvinylpyrrolidone (PVP) (blue), the absorbance around 525 nm was found to be negligibly small, while PSS- showed high absorbance at 525 nm (violet) and above 700 nm (oxidized PEDOT). PSS- also allows complete oxidation of EDOT and serves as an effective dopant for PEDOT. While AuNPs covered by PEDOT alone cannot be dispersed in aqueous solutions, PSS- renders Au-PEDOT water soluble. The hydrodynamic diameter of the nanocomposite estimated from the dynamic light scattering (DLS) measurements increases in the order Na-PSS < SDS < PVP. Interestingly, the color of the Au(nano)-PEDOT/PSS- aqueous dispersion changed reversibly between violet and blue and vice versa on addition of NaOH and HCl, respectively. This reversible color change appears to be a combination effect of acid/base on the properties of PEDOT, in turn changing the environment around the embedded AuNPs. The nanoparticle dispersion also exhibited very high stability in presence of 3.0 M NaCl. Remarkably, the nanocomposite Au(nano)-PEDOT/PSS- was found to function as an effective catalyst to activate the reduction of 4-nitrophenol to 4-aminophenol in the presence of excess NaBH4, and the calculated apparent rate constant value of 4.39 x 10-2 s-1 is found to be higher than those obtained using other nanocomposites with SDS and PVP and comparable to the values reported in the case of other encapsulants.