Carbon nanodots as reductant and stabilizer for one-pot sonochemical synthesis of amorphous carbon-supported silver nanoparticles for electrochemical nonenzymatic H2O2 sensing

Using Nanomaterials as Excellent Immobilisation Layer for Biosensor Design

The endless development in nanotechnology has introduced new vitality in device fabrication including biosensor design for biomedical applications. With outstanding features like suitable biocompatibility, good electrical and thermal conductivity, wide surface area and catalytic activity, nanomaterials have been considered excellent and promising immobilisation candidates for the development of high-impact biosensors after they emerged. Owing to these reasons, the present review deals with the efficient use of nanomaterials as immobilisation candidates for biosensor fabrication. These include the implementation of carbon nanomaterials-graphene and its derivatives, carbon nanotubes, carbon nanoparticles, carbon nanodots-and MXenes, likewise their synergistic impact when merged with metal oxide nanomaterials. Furthermore, we also discuss the origin of the synthesis of some nanomaterials, the challenges associated with the use of those nanomaterials and the chemistry behind their incorporation with other materials for biosensor design. The last section covers the prospects for the development and application of the highlighted nanomaterials.

Application of Low-Cost Plant-Derived Carbon Dots as a Sustainable Anode Catalyst in Microbial Fuel Cells for Improved Wastewater Treatment and Power Output

Microbial fuel cells (MFC) can generate electric energy from wastewater which can be enhanced further by anode catalysts. The recovery of electrons produced by oxidation of organics catalyzed by bacteria in the anode was enhanced when carbon dots(CDs) were added into the MFC. In this present study, a novel strategy for designing anode material and the fabrication of a high-efficient and environmentally friendly anode for energy generation from wastewater was reported. The CDs were synthesized by the pyrolysis of a peanut shell at the temperature of 250 °C for 2 h with a heating rate of 10 °C min−1. Thus synthesized CDs were characterized by transmission electron microscopy (TEM), UV/Vis spectroscopy, and fluorescence spectroscopy. The TEM analysis showed morphology with an average size of 1.62 nm. The UV/Vis absorbance of the CDs shows a wide absorption band without a characteristic peak. The excitation spectrum of CDs recorded at the emission wavelength of 440 nm exhibits a peak around 320 nm. CDs were investigated as an anode material in a MFC utilizing acetate as the organic substrate. The average chemical oxygen demand (COD) removal in closed circuit operation mode was 89%. The maximum power density production (7.2 W/m3) was observed in MFC containing 1 mg/cm2 CD-impregnated anode (CDsIA). The CDsIA provides the ability to promote efficient biofilm formation. These results emphasize the application of CD-based electrodes in MFCs for the simultaneous treatment of wastewater and electricity generation while also providing additional benefits.

An Exfoliated Graphite-Based Electrochemical Immunosensor on a Dendrimer/Carbon Nanodot Platform for the Detection of Carcinoembryonic Antigen Cancer Biomarker

An electrochemical immunosensor for the quantification of carcinoembryonic antigen (CEA) using a nanocomposite of polypropylene imine dendrimer (PPI) and carbon nanodots (CNDTs) on an exfoliated graphite electrode (EG) is reported. The carbon nanodots were prepared by pyrolysis of oats. The nanocomposites (PPI and CNDTs) were characterized using X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The proposed immunosensor was prepared on an exfoliated graphite electrode sequentially by drop coating CNDTs, the electrodeposition of G2-PPI (generation 2 poly (propylene imine) dendrimer), the immobilization of anti-CEA on the modified electrode for 80 min at 35 °C, and dropping of bovine serum albumin (BSA) to minimize non-specific binding sites. Cyclic voltammetry was used to characterize each stage of the fabrication of the immunosensor. The proposed immunosensor detected CEA within a concentration range of 0.005 to 300 ng/mL with a detection limit of 0.00145 ng/mL by using differential pulse voltammetry (DPV). The immunosensor displayed good stability and was also selective in the presence of some interference species such as ascorbic acid, glucose, alpha-fetoprotein, prostate-specific antigen and human immunoglobulin. Furthermore, the fabricated immunosensor was applied in the quantification of CEA in a human serum sample, indicating its potential for real sample analysis.

A nanocomposite of N-doped carbon dots with gold nanoparticles for visible light active photosensitisers

N-Doped carbon dots (N-CDs) from tannic acids showed a capability to act as visible light active photosensitisers. The photosensitizing efficiency of N-CDs was enhanced by the conjugation with gold nanoparticles.

Sustained and Cost Effective Silver Substrate for Surface Enhanced Raman Spectroscopy Based Biosensing

While surface enhanced Raman spectroscopy (SERS) based biosensing has demonstrated great potential for point-of-care diagnostics in the laboratory, its application in the field is limited by the short life time of commonly used silver based SERS active substrates. In this work, we report our attempt towards SERS based field biosensing, involving the development of a novel sustained and cost-effective substrate composed of silver nanoparticles protected by small nitrogen-doped Graphene Quantum Dots, i.e. Ag NP@N-GQD, and its systematic evaluation for glucose sensing. The new substrate demonstrated significantly stronger Raman enhancement compared to pure silver nanoparticles. More importantly, the new substrate preserved SERS performance in a normal indoor environment for at least 30 days in both the wet and dry states, in contrast to only 10 days for pure silver nanoparticles. The Ag NP@N-GQD thin film in the dry state was then successfully applied as a SERS substrate for glucose detection in mouse blood samples. The new substrate was synthesized under mild experimental conditions, and the cost increase due to N-GQD was negligible. These results suggest that the Ag NP@N-GQD is a cost-effective and sustained SERS substrate, the development of which represents an important step towards SERS based field biosensing.

Carbon quantum dots shuttle electrons to the anode of a microbial fuel cell

Electrodes based on graphite, graphene, and carbon nanomaterials have been used in the anode chamber of microbial fuel cells (MFCs). Carbon quantum dots (C-dots) are a class of versatile nanomaterials hitherto not reported in MFCs. C-dots previously synthesized from coconut husk were reported to possess hydroxyl and carboxyl functional groups on their surface. The presence of these functional groups on a carbon matrix conferred on the C-dots the ability to conduct and transfer electrons. Formation of silver nanoparticles from silver nitrate upon addition of C-dots confirmed their reducing ability. DREAM assay using a mixed microbial culture containing C-dots showed a 172% increase in electron transfer activity and thus confirmed the involvement of C-dots in supplementing redox activity of a microbial culture. Addition of C-dots as a suspension in the anode chamber of an MFC resulted in a 22.5% enhancement in maximum power density. C-dots showed better performance as electron shuttles than methylene blue, a conventional electron shuttle used in MFCs.

Synthesis and size-dependent electrochemical nonenzymatic H2O2 sensing of cuprous oxide nanocubes

The smaller size Cu₂O nanocubes can effectively increase the electrocatalytic active areas and subsequently promote electron transfer in the reduction of H₂O₂.