Fabrication of colorimetric sensor using Fe3O4 @ Musa paradisiaca L. nanoparticles for detecting hydrogen peroxide: an application in environmental and biological samples

Evolution and recent development of cellulose-modified, nucleic acid-based and green nanosensors for trace heavy metal ion analyses in complex media: A review

With increased manufacturing activities and energy sector development, monitoring of heavy metal ion (HMI) pollution is becoming increasingly pressing. The discharge of metals from industrial effluents into the waterways could cause major economic and environmental disruption. In situ and on-site detection methods of trace HMIs can be effective countermeasures before the toxicity spreads out to larger areas, affecting the ecosystem. Conventional methods are often lacking in portability and costly. In contrast, electrochemical sensing, especially with nanoplatforms, is promising for trace detection of HMIs in complex media because of the ease of fabrication and adaptability of incorporating green technology. Appropriate electrode selection with suitable modifiers is crucial in complex medium analyses to overcome electrode fouling. In this review, the evolution from metal-based and carbon-based electrodes to advancements in electrode modification involving agro/biocomposite nanomaterials (NMs) such as cellulose, chitosan, and hydroxyapatite is discussed. The fabrication of nucleic acid-based aptasensors for analyzing HMIs and the adoption of smart systems based on microfluidics with high selectivity, operational stability, and sensitivity are highlighted. The challenges and future prospects for trace HMI determination based on electrochemical sensors in real complex media, including blood and industrial effluent or wastewater, are critically examined.

On-demand activatable peroxidase-mimicking enzymatic polymer nanocomposite films

Nanozymes continue to attract considerable attention to minimise the dependence on expensive enzymes in bioassays, particularly in medical diagnostics. While there has been considerable effort directed towards developing different nanozymes, there has been limited progress in fabricating composite materials based on such nanozymes. One of the biggest gaps in the field is the control, tuneability, and on-demand catalytic response. Herein, a nanocomposite nanozymatic film that enables precise tuning of catalytic activity through stretching is demonstrated. In a systematic study, we developed poly(styrene-stat-n-butyl acrylate)/iron oxide-embedded porous silica nanoparticle (FeSiNP) nanocomposite films with controlled, highly tuneable, and on-demand activatable peroxidase-like activity. The polymer/FeSiNP nanocomposite was designed to undergo film formation at ambient temperature yielding a highly flexible and stretchable film, responsible for enabling precise control over the peroxidase-like activity. The fabricated nanocomposite films exhibited a prolonged FeSiNP dose-dependent catalytic response. Interestingly, the optimised composite films with 10 wt% FeSiNP exhibited a drastic change in the enzymatic activity upon stretching, which provides the nanocomposite films with an on-demand performance activation characteristic. This is the first report showing control over the nanozyme activity using a nanocomposite film, which is expected to pave the way for further research in the field leading to the development of system-embedded activatable sensors for diagnostic, food spoilage, and environmental applications.

Decorating Zirconium on Graphene Oxide to Design a Multifunctional Nanozyme for Eco-Friendly Detection of Hydrogen Peroxide

Peroxidase enzymes are crucial in analytical chemistry owing to significant peroxide analytes and their key role in hydrogen peroxide (H2O2) detection. Therefore, exploiting appropriate catalysts for the peroxidase like reactions has become crucial for achieving desired analytical performance. Zirconium (Zr) has attracted growing interest, as a safe and stable potential eco-friendly catalyst for various organic transformations that address increasing environmental challenges. Hence, aiming at fast, sensitive and selective optical detection of H2O2, a colorimetric platform is presented here, based on the excellent peroxidase enzyme-like activity of Zr decorated on graphene oxide (GO). The synergistic effect achieved due to intimate contact between an enzyme like Zr and the high surface area 0f GO ensures efficient electron transfer that increases the chemical and catalytic activity of the composite and advances the decomposition of H2O2 into hydroxyl radicals. The designed probe, thus, efficiently catalyzes the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB), via hydroxyl radicals, thereby transforming the colorless TMB into blue oxidized TMB within 2 min. The catalytic mechanism of the Zr-GO enzyme mimic is proposed herein and verified using a fluorescent probe terephthalic acid (TA) and other scavenger experiments. The multifunctional optical probe allows sensitive and highly selective recognition of H2O2 in a linear range from 100 to 1000 µM with a low detection limit of 0.57 µM. Essentially, the direct accessibility of Zr prevents having to use the complicated preparation and purification procedures mostly practiced for conventional biozymes and nanozymes. The devised method offers several gains, including being green and an inexpensive catalyst, having lower LOD, being fast, cost-effective and sensitive, and having selective work-up procedures.