Ultrasonication-assisted synthesis of transition metal carbide of MXene: an efficient and promising material for photocatalytic organic dyes degradation of rhodamine B and methylene blue in wastewater.

Water pollutants of non-biodegradable toxic aromatic dye including Methylene blue (MB) and Rhodamine (RhB) are extremely carcinogenic thiazines used in various industries such as leather industry, paper industry, and the dyeing industry. The presence of dyes in wastewater causes severe threats to human health that are responsible for various harmful chronic or acute diseases and also shows an adverse impact on the environment as it reduces transparency and is harmful to water microorganisms. To overcome severe issues, many traditional techniques have been used to remove toxic pollutants, but these methods are insufficient to remove chemically stable dyes that remain in the treated wastewater. However, the photocatalytic degradation process is an efficient approach to degrade the dye up to the maximum extent with improved efficiency. Therefore, in this work, a new class of two-dimensional (2D) transition metal carbide of Titanium Carbide (Ti3C2Tx) MXene material was used for the organic dyes degradation such as MB and RhB using a photocatalytic process. A layered structure of hexagonal lattice symmetry of Ti3C2Tx MXene was successfully synthesized from the Titanium Aluminum Carbide of Ti3AlC2 bulk phase using an exfoliation process. Further, the XRD spectrum confirms the transformation of bulk MAX phase having (002) plane at 9.2° to Ti3C2Tx MXene of (002) plane at 8.88° confirms the successful removal of Al layer from MAX phase. A smooth, transparent, thin sheet-like morphology of Ti3C2Tx nanosheet size were found to be in the range of 70 to 150 nm evaluated from TEM images. Also, no holes or damages in the thin sheets were found after the treatment with strong hydrofluoric acid confirms the formation Ti3C2Tx layered sheets. The synthesized Ti3C2Tx MXene possesses excellent photocatalytic activity for the degradation of dyes MB, RhB, and mixtures of MB and RhB dyes. MB dye degraded with a degradation percentage efficiency of 99.32% in 30 min, while RhB dye was degraded upto 98.9% in 30 min. Also, experiments were conducted for degradation of mixture of MB and RhB dyes by UV light, and the degradation percentage efficiency were found to be 98.9% and 99.75% for mixture of MB and RhB dye in 45 min, respectively. Moreover, reaction rate constant (k) was determined for each dye of MB, RhB, and mixtures of MB and RhB and was found to be 0.0215 min-1 and 0.0058 min-1, and for mixtures, it was 0.0020 min-1 and 0.009 min-1, respectively.

Graphene oxide-Mn3O4nanocomposites for advanced electrochemical biosensor for fumonisin B1 detection.

Occurrence of mycotoxins in food samples threat to its safety issue due to the presence of high toxicity and carcinogenic behavior, thus requiring highly sensitive and selective detection. Herein, the trimanganese tetraoxide (Mn3O4) nanoparticles in combination with graphene oxide (GO) nanocomposite were used to enhance the electrochemical performance for fabrication of electrochemical biosensor for fumonisin B1 (FB1) detection. The various characterization tools were used to validate the fabrication of GOMn3O4nanocomposites. To fabricate the electrochemical biosensor on an indium tin oxide (ITO) coated glass substrate, a thin film of GOMn3O4nanocomposite was prepared using electrophoretic deposition technique, and antibodies (ab-FB1) were immobilized onto the electrode for selective FB1 detection. The differential pulse voltammetry technique was used to observe the sensing performance. The non-binding sites of the ab-FB1 on the immunoelectrode were blocked with bovine serum albumin (BSA). The biosensor electrode was fabricated as BSA/ab-FB1/GOMn3O4/ITO for the detection of FB1. The sensitivity of the biosensor was obtained as 10.08µA ml ng-1cm-2in the detection range of 1 pg ml-1to 800 ng ml-1with a limit of detection of 0.195 pg ml-1. In addition, the recovery of BSA/ab-FB1/GOMn3O4/ITO immunoelectrodes was also performed on sweet corn samples and is calculated to be 98.91%.

Recent advances in nanomaterials integrated immunosensors for food toxin detection.

For the management and prevention of many chronic and acute diseases, the rapid quantification of toxicity in food and feed products have become a significant concern. Technology advancements in the area of biosensors, bioelectronics, miniaturization techniques, and microfluidics have shown a significant impact than conventional methods which have given a boost to improve the sensing performance towards food analyte detection. In this article, recent literature of Aflatoxin B1 (AFB1), worldwide permissible limits, major outbreaks and severe impact on healthy life have been discussed. An improvement achieved in detection range, limit of detection, shelf-life of the biosensor by integrated dimensional nanomaterials such as zero-dimension, one-dimension and two-dimension for AFB1 detection using electrical and optical transduction mechanism has been summarized. A critical overview of the latest trends using paper-based and micro-spotted array integrated with the anisotropic shape of nanomaterials, portable microfluidic devices have also been described together with future perspectives for further advancements.

Gold nanobipyramids integrated ultrasensitive optical and electrochemical biosensor for Aflatoxin B1 detection.

This work reports the development of an electrical and optical biosensing for label-free detection of Aflatoxin B1 (AFB1) using gold (Au) nanobipyramids (NBPs). AuNBPs were synthesized through a two-step seed-mediated growth process followed by an exchange of capping agent from surfactant to lipoic acid. Pure and monodispersed AuNBPs of 70 nm base length were obtained and deposited on indium tin oxide (ITO)-coated glass substrate modified with self-assembled (3-Aminopropyl) triethoxysilane (APTES) film. The characterization of the obtained surfaces using spectroscopy, microscopy and diffractometry confirms the formation of AuNBPs, the conjugation to ITO electrode substrate and the immobilization of anti-AFB1 antibodies. AuNBPs modified ITO substrates were used for both electrochemical and Surface Plasmon Resonance biosensing studies. Localized Surface Plasmon Resonance (LSPR) local field enhancement was demonstrated. SPR based AFB1 detection was found to be linear in the 0.1-500 nM range with a limit of detection of 0.4 nM, whereas, impedimetric AFB1 detection was shown to be linear in the 0.1-25 nM range with a limit of detection of 0.1 nM. The practical utility of the impedimetric sensor was tested in spiked maize samples and 95-100% recovery percentage was found together with low relative standard deviation, proof of the robustness of this AFB1 sensor.

Integrated graphene quantum dot decorated functionalized nanosheet biosensor for mycotoxin detection.

Decoration of graphene quantum dots (GQDs) on molybdenum disulfide (MoS2) nanosheets serves as an active electrode material which enhances the electrochemical performance of the analyte detection system. Herein, ionic surfactant cetyltrimethylammonium bromide (CTAB)-exfoliated MoS2 nanosheets decorated with GQD material are used to construct an electrochemical biosensor for aflatoxin B1 (AFB1) detection. An antibody of AFB1 (aAFB1) was immobilized on the electrophoretically deposited MoS2@GQDs film on the indium tin oxide (ITO)-coated glass surface using a crosslinker for the fabrication of the biosensor. The immunosensing study investigated by the electrochemical method revealed a signal response in the range of 0.1 to 3.0 ng/mL AFB1 concentration with a detection limit of 0.09 ng/mL. Also, electrochemical parameters such as diffusion coefficient and heterogeneous electron transfer (HET) were calculated and found to be 1.67 × 10-5 cm2/s and 2 × 10-5 cm/s, respectively. The effective conjugation of MoS2@GQDs that provides abundant exposed edge sites, large surface area, improved electrical conductivity, and electrocatalytic activity has led to an excellent biosensing performance with enhanced electrochemical parameters. Validation of the fabricated immunosensor was performed in a spiked maize sample, and a good percentage of recoveries within an acceptable range were obtained (80.2 to 98.3%).Graphical abstract.

A label-free ultrasensitive microfluidic surface Plasmon resonance biosensor for Aflatoxin B1 detection using nanoparticles integrated gold chip.

The Surface Plasmon resonance (SPR) based label-free detection of small targeted molecules is a great challenge and require substantial signal amplification for the accurate and precise quantification. The incorporation of noble metal nanoparticles (NPs) like gold (Au) NPs for the fabrication of SPR biosensor has shown remarkable impact both for anchoring the signal amplification and generate plasmonic resonant coupling between NPs and chip surface. In this work, we present comparative studies related to the fabrication of self-assembled monolayer (SAM) and the influence of AuNPs on Au chip for Aflatoxin B1 (AFB1) detection using SPRi apparatus. The SAM Au chip was sequentially modified by EDC-NHS crosslinkers, grafting of protein-A and finally interaction with anti-AFB1 antibodies. Similar multilayer chip surface was prepared using functionalized lipoic acid AuNPs deposited on SAM Au chips followed by in situ activation of functional groups using EDC-NHS crosslinkers, grafting of protein-A and immobilization of anti-AFB1 antibodies. This multilayer functionalized AuNPs modified Au chip was successfully utilized for AFB1 detection ranging from 0.01 to 50 nM with a limit of detection of 0.003 nM. When compared to bare self-assembled Au chip which was shown to exhibit a limit of detection of 0.19 nM and a linear detection ranging from 1 to 50 nM, the AuNPs modified Au chip was proven to clearly be a better analytical tool. Finally, validation of the proposed biosensor was evaluated by spiked wheat samples and average recoveries (93 and 90.1%) were found to be acceptable.

Electrochemical Aflatoxin B1 immunosensor based on the use of graphene quantum dots and gold nanoparticles.

Electrochemical immunosensor for aflatoxin B1 (AFB1) is described that uses a composite prepared from graphene quantum dots (GQDs) and gold nanoparticles (Au NPs). The GQD-AuNP conjugate was obtained by using 2-aminothiophenol (ATP) as a linker where the carboxy groups of GQD bind to the amino groups of crosslinker via conjugation of thiol binding to the AuNP. To evaluate the conjugation of the GQD-AuNP composite, Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM) was applied. The composite was placed on an indium tin oxide (ITO) electrode and then modified with an antibody against AFB1. By using hexacyanoferrate as the electrochemical probe, the sensor works in the 0.1 to 3.0 ng mL-1 AFB1 concentration range, is highly specific, has good reproducibility and acceptable stability. The biosensor was applied to the analysis of (spiked) maize samples. Conceivably, the method can be utilized to sense other mycotoxins by using their respective antibodies. Graphical abstract Schematic presentation of electrochemical immunosensor for Aflatoxin B1 (AFB1) detection developed by antibodies of AFB1 (anti-AFB1) immobilization on graphene quantum dots (GQDs)-gold nanoparticles (AuNPs) composite deposited by electrophoretic deposition technique on an Indium tin oxide (ITO) surface.

Development of electrochemical biosensor based on CNT-Fe3O4 nanocomposite to determine formaldehyde adulteration in orange juice.

An electrochemical biosensor was developed to determine formaldehyde (HCHO) adulteration commonly found in food. The current responses of various electrodes based on multiwalled carbon nanotubes (CNTs) and synthesized nanocomposite (CNT-Fe3O4) were measured using cyclic voltammetry. The nanocomposite based biosensor shows comparatively high sensitivity (527 µA mg/L-1 cm-2), low detection limit (0.05 mg/L) in linear detection range 0.05-0.5 mg/L for formaldehyde detection using formaldehyde dehydrogenase (FDH) enzyme. In real sample analysis, the low obtained RSD values (less than 1.79) and good recovery rates (more than 90%) signify an efficient and precise sensor for the selective quantification of formaldehyde in orange juice. The developed biosensor has future implications for determining formaldehyde adulteration in citrus fruit juices and other liquid foods in agri-food chain to further resolve global food safety concerns, control unethical business practices of adulteration and reduce the widespread food borne illness outbreaks.

Graphene quantum dots-based nano-biointerface platform for food toxin detection.

Due to the similar electrochemical properties to graphene oxide (GO), graphene quantum dots (GQDs) are considered as a highly potential candidate for designing an electrochemical biosensor. In this report, GQDs were synthesized having an average diameter of 7 nm and utilized for the fabrication of an electrochemical immunosensor for the detection of food toxin, aflatoxin B1 (AFB1). An electrophoretic deposition technique was utilized to deposit the chemically synthesized GQDs onto indium tin oxide (ITO)-coated glass substrate. Further, the monoclonal antibodies of AFB1 were covalently immobilized onto deposited electrode GQDs/ITO using EDC-NHS as a crosslinker. The structural and morphological studies of GQDs and conjugated anti-AFB1 with GQDs have been investigated using UV-visible spectroscopy, photoluminescence spectroscopy, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy techniques, etc. The electrochemical impedance spectroscopy and cyclic voltammetry measurements were carried out for electrical characterization and biosensing studies. This simple monodisperse GQDs-based platform yields heterogeneous electron transfer (97.63 × 10-5 cm s-1), the time constant (0.005 s) resulting in improved biosensing performance. The electrochemical immunosensor shows high sensitivity 213.88 Ω (ng mL-1)-1 cm-2. The limit of detection for standard samples and contaminated maize samples was found to be 0.03 ng mL-1 and 0.05 ng g-1, respectively, which is lower than the maximum acceptable limit according to the European Union. This result indicates its potential application for aflatoxin B1 detection in food contents. Graphical abstract ᅟ.