Electrochemical determination of adenine using a glassy carbon electrode modified with graphene oxide and polyaniline

Carbon-Based Nanocomposite Smart Sensors for the Rapid Detection of Mycotoxins

Carbon-based nanomaterials have become the subject of intensive interest because their intriguing physical and chemical properties are different from those of their bulk counterparts, leading to novel applications in smart sensors. Mycotoxins are secondary metabolites with different structures and toxic effects produced by fungi. Mycotoxins have low molecular weights and highly diverse molecular structures, which can induce a spectrum of biological effects in humans and animals even at low concentrations. A tremendous amount of biosensor platforms based on various carbon nanocomposites have been developed for the determination of mycotoxins. Therefore, the contents of this review are based on a balanced combination of our own studies and selected research studies performed by academic groups worldwide. We first address the vital preparation methods of biorecognition unit (antibodies, aptamers, molecularly imprinted polymers)-functionalized carbon-based nanomaterials for sensing mycotoxins. Then, we summarize various types of smart sensors for the detection of mycotoxins. We expect future research on smart sensors to show a significant impact on the detection of mycotoxins in food products.

Portable electrochemical immunosensor for detection of Mycobacterium tuberculosis secreted protein CFP10-ESAT6 in clinical sputum samples

An early detection of Mycobacterium tuberculosis is very important to reduce the number of fatal cases and allow for fast recovery. However, the interpretation of the result from smear microscopy requires skilled personnel due to the propensity of the method to produce false-negative results. In this work, a portable, rapid, and simple sandwich-type immunosensor reader has been developed that is able to detect the presence of M. tuberculosis in sputum samples. By using sandwich-type immunosensor, an anti-CFP10-ESAT6 antibody was immobilized onto the graphene/polyaniline (GP/PANI)-modified gold screen-printed electrode. After incubation with the target CFP10-ESAT6 antigen, the iron/gold magnetic nanoparticles (Fe₃O₄/Au MNPs) conjugated with anti-CFP10-ESAT6 antibody were used to complete the sandwich format. Differential pulse voltammetry (DPV) technique was used to detect the CFP10-ESAT6 antigen at the potential range of 0.0-1.0 V. The detection time is less than 2 h. Under optimal condition, CFP10-ESAT6 antigen was detected in a linear range from 10 to 500 ng mL^-1 with a limit of detection at 1.5 ng mL^-1. The method developed from this process was then integrated into a portable reader. The performance of the sensor was investigated and compared with the standard methods (culture and smear microscopy). It provides a good correlation (100% sensitivity and 91.7% specificity) with both methods of detection for M. tuberculosis in sputum samples henceforth, demonstrating the potential of the device as a more practical screening tool.Graphical abstract.

Ultra-sensitive electrochemical aptasensor for label-free detection of Aflatoxin B1 in wheat flour sample using factorial design experiments

Considering the significance of mycotoxin detection in food industries, herein, an ultrasensitive aptasensor was developed based on aflatoxin B1 aptamer immobilized on Carbon quantum dots/octahedral Cu₂O nanocomposite. Electrochemical measurements were based on Electrochemical Impedance Spectroscopy (EIS) and Differential Pulse Voltammetry (DPV). Since the effective parameters (pH, temperature, incubation time and concentration of aptamers) are interdependent, so their dependent study can be nonideal. Taguchi method has solved this problem and optimized the experimental conditions using a smaller number of experiments. Under optimum conditions, the electrochemical signals declined as AFB1 concentrations increased with a dynamic range of 3 ag.ml^-1 -1.9 µg.ml^-1 and a low limit of detection (LOD) of 0.9 ± 0.04 ag ml^-1. The obtained results proved sufficient repeatability (RSD = 2.4%), reproducibility (RSD = 2.56%), accuracy (97.2-104.4% recovery), and robustness (RSD = 3.25%). Furthermore, considerable selectivity, stability and reliability of the aptasensor confirmed the capability to work in future real assays.

Swollen liquid crystalline mesophase assisted synthesis of GO-PANI nanocomposite as a fluorescent probe for purines

This article focuses on the use of graphene oxide-polyaniline (GO-PANI) nanocomposite as fluorescent probe for sensing of adenine (A) and guanine (G). Swollen liquid crystalline mesophase were used for the synthesis of graphene oxide-polyaniline nanocomposite. GO-PANI nanocomposite showed enhanced fluorescent at 441 nm (ƛ _excitation = 361 nm) on interaction of purines viz A and G solutions in dimethyl sulfoxide, GO exhibited quenching at 540 nm (ƛ _excitation = 261 nm). The fluorescence emission spectra of GO-PANI nanocomposite and GO were recorded in the the pressence of A and G concentrations upto 1.2 × 10^-4 M. The limits of detection (LOD) calculated from the concentration dependence study for GO-PANI nanocomposite and GO are 7.5 × 10^-6 M and 13.4 × 10^-6 M respectively. The LOD in the case of GO is identical for both A (13.0 × 10^-6) and G (13.6 × 10^-6 M). The binding constant (K_b) determined for GO-PANI with purines are in the range of 0.05-0.08 × 10³ M^-1 which is higher in the case of GO (2.42-7.52 × 10³ M^-1). The lifetime measurement demonstrates, an excited state interaction of GO-PANI nanocomposite and GO with purines. This is evident from the increasing lifetime from 4.3 ns to 29.2 ns for GO-PANI nanocomposite, while 17.5 ns to 37.2 ns for GO respectively. The relatively short lifetime of the GO-PANI nanocomposite in comparison with GO suggest an electronic charge dissipation of the excited state between polyaniline and graphene oxide possibly due to the alignment of polyaniline on the graphene oxide sheet. The photopysical properties of GO-PANI nanocomposite and GO observed in this study is new and has potential for application as fluorescent probe for the detection of purines.

Fabrication of a sensitive electrochemical sensor based on electrospun magnetic nanofibers for morphine analysis in biological samples

A sensitive electrochemical sensor for detection of morphine (MPH) at the surface of electrode modified with electrospun magnetic nanofibers (MNFs) was prepared. The features of constructed sensor were evaluated by scanning electron microscopy (SEM), X ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS). The modified sensor was used for MPH analysis using of cyclic voltammetry (CV) and differential pulse voltammetry (DPV) method. The calibration curve has been composed of a linear portion in the concentration range of 0.0033-55 μM and 55-245 μM and the detection limit was 1.9 nM. The reproducibility of the peak current with a reliable relative standard deviation (RSD) value was acquired. Based on the results, the fabricated sensor has good stability and reproducibility, as well as the sensitive and selective analysis of MPH in human serum samples as real samples had effectively been feasible. The results of the actual sample were measured by HPLC procedure, and the results were compared with the results of the electrochemical method and corroborated them.