Morphology Effect of One-Dimensional MnO2 Nanostructures on Heteroatom-Doped Carbon Dot-Based Biosensors for Selective Detection of Glutathione

Structural versatility of MnO₂ nanostructures plays a significant role in biosensing applications. So, we have prepared simple and selective "turn-off-on" sensing probes for the detection of glutathione (GSH), based on nitrogen, sulfur codoped carbon dots (N, S-Cdots) and different morphologies of one-dimensional (1-D) MnO₂ nanostructures. N, S-Cdots with a high fluorescence quantum yield (73.42%) were prepared by a green approach through high-temperature pyrolysis in just 5 min. The different morphologies of 1-D MnO₂ nanostructures (nanowires with varying aspect ratios and nanorods) were synthesized through a hydrothermal method by varying the reaction period (8, 10, and 12 h). MnO₂ nanowires prepared at 8 h showed a high specific surface area (34 m² g^-1) with a large aspect ratio. They showed significant fluorescence quenching, Stern-Volmer constants, and binding constants in the presence of N, S-Cdots. Further, ultraviolet-visible absorption, zeta potential, and time decay studies showed that the quenching mechanism of the developed sensing system was the inner filter effect, which was further confirmed by using the Parker equation. The N, S-Cdots-MnO₂ nanowire (with a high aspect ratio) sensing system showed the best limit of detection, i.e., 28.5 μM for GSH. This fast, simple, eco-friendly, and cost-effective sensing system can be further used for real-time biosensing and bioimaging application.

Morphology-Dependent Performance of MnO2 Nanostructure-Carbon Dot-Based Biosensors for the Detection of Glutathione

Herein, we develop a facile, sensitive, and selective fluorescent nanosensor for the detection of glutathione (GSH). In this protocol, carbon dots (Cdots) with a fairly high quantum yield were synthesized by a microwave-assisted pyrolysis technique. Moreover, different shapes of the MnO₂ nanostructure were also prepared by the hydrothermal technique. A comparative photophysical study of different morphology-dependent Cdots@MnO₂ nanostructure-based biosensors was explored, which showed different results for the quenching values of ("turn-off") fluorescence intensity, quantum yields, electron transfer rate, and average lifetime. The structure, property, and performance of nanomaterials are interdependent. Therefore, the different shapes of MnO₂, that is, nanoflowers (NFs), nanorods (NRs), and a mixture of NFs/NRs was prepared by the hydrothermal method owing to different specific surface areas (23-69 m² g^-1) which put the impact on their sensing activity. It was observed that the variation in the different photophysical parameters of fluorescent Cdots such as quantum yield (Φ), average lifetime values [τ_av (ns)], radiative (k_r) rate constant, nonradiative (k_nr) rate constant, rate of electron transfer (k_ET), the efficiency of electron transfer (Φ_EET), FRET efficiency (E), and Förster distance (R₀) were dependent on the different shapes of the MnO₂ nanostructure. These results indicate that the transfer of energy occurs between the Cdots and different shapes of MnO₂ nanostructures based on fluorescence resonance energy transfer at different charge-transfer rates. The recovery rate ("turn-on") of fluorescence of Cdots with the addition of GSH was obtained best for the NF structure by conversion of MnO₂ to Mn²⁺, and the limit of detection was obtained as ∼19 μM for GSH. The developed sensing probes were rapid, easy, cheap, and eco-friendly for the determination of GSH.

Fabrication of highly stable platinum organosols over DNA-scaffolds for enriched catalytic and SERS applications

The use of nanomaterials (NMs) in various applications via multidisciplinary approaches is highly necessary in this era. In this line, the impact of noble metals in organic media for both catalysis and surface-enhanced Raman spectroscopic (SERS) studies is most interesting and also has a wider scope in various fields. Nonetheless, the catalytic reduction of aromatic nitro compounds is difficult with poor solubility in aqueous media, and reduction also is less feasible in the absence of noble metal-based catalysts. Thus, the choice of noble metal-based catalysts for the catalytic reduction of nitro compounds in organic media is one of the emerging methods with high selectivity towards products. Moreover, the superior catalytic activity of Pt NPs provides a higher rate constant value with a low dielectric constant of organic solvents. Herein, for the first time, we synthesised highly stable metallic Pt nanoparticles (NPs) anchored on bio-scaffold deoxyribonucleic acid (DNA) for two different applications. The advantage of highly controlled nucleation of NPs over DNA in organic media results in a spherical morphology with a particle diameter of 2.47 ± 2.11 nm and 2.84 ± 1.14 nm. A stable colloidal solution of Pt NPs was prepared by a simple wet chemical sodium borohydride reduction method within 15 minutes from the start of the reaction. Two sets of Pt NPs were synthesised by varying the molar ratio of the concentration of DNA to PtCl4 concentration and were named Pt@DNA (0.05 M) and Pt@DNA (0.06 M), respectively. The prepared Pt@DNA was effectively studied for two potential applications such as the SERS studies and catalytic reduction of nitro compounds. In catalysis, a higher catalytic rate was observed in the case of 4-nitrophenol (4-NP) at a rate of 8.43 × 10-2 min-1. In the SERS study, the reduction of the interparticle distance to below 5 nm facilitates the creation of a large number of hot spots for probe detection. Here, we used 10-3 M methylene blue (MB) as a probe molecule, and the enhancement factor (EF) value was calculated at different concentrations ranging from 10-3 M to 10-6 M. The highest enhancement factor (EF) value obtained was 2.91 × 105 for Pt@DNA (0.05 M). The as-synthesised stable Pt@DNA organosol can be exploited for other potential applications related to energy, sensor and medicinal fields in the near future.

Prospects in interfaces of biomolecule DNA and nanomaterials as an effective way for improvising surface enhanced Raman scattering: A review

Surface Enhanced Raman Scattering (SERS) is a field of research that has shown promising application in the analysis of various substrate molecules by means of rough metallic surfaces. In directing the enhancement of substrate molecules in micro and nano-molar concentrations, plasmonic coupling of metal nanoparticles (NPs), morphology of metal NPs and the closely arrangement of rough metal surfaces that produces 'hot spots' can effectively increase the so-called enhancement factor (EF) that will be applicable in various fields. As the mechanistic aspects are still not clear, research has been triggered all over the world for the past two decades to have a clear understanding in chemical and electromagnetic effects. As the reproducibility of intensity of signals at low concentrations of probe molecules is of a big concern, metal NPs with various scaffolds were prepared and recently bio-molecule, DNA has been studied and showed promising advantages. This review first time highlights metal NPs with DNA interface as an effective rough metallic surface for SERS with high intensity and also with better reproducibility. Based on this review, similar kinds of scaffolds like DNA can be used to further analyze SERS activities of various metal NPs with different morphologies to have high intense signals at low concentrations of probe molecules.

Developments in DNA metallization strategies for water splitting electrocatalysis: A review

The biomolecule DNA with the presence of different functionalities found to interact with different kinds of metal ions and show relatively higher stability over a long period of time when optimized appropriately. With the presence of A-T and G-C pairs, sugar moieties, phosphate functional groups and the double-helical structure, it can assemble both cationic and anionic species and forms a perfect metal-DNA self-assembly. Depending upon the aspect ratio of metal-DNA self-assemblies, metal content and their morphological outcomes, they could deliver variance in the catalytic activities. Such differences can be brought out by varying the synthesis reaction parameters focusing on a specific electrocatalytic application. In this review, recent developments in DNA metallization is elaborated first highlighting the underlying interactions between DNA and cationic/anionic species of various metals following which application of metal-DNA assemblies in electrocatalytic water oxidation and reduction are discussed critically. Knowledge provided in this review thus acts as the guide to various DNA metallization strategies and their subsequent application to water electrolysis for hydrogen generation.

A Surfactant Directed Microcrystalline Cellulose/Polyaniline Composite with Enhanced Electrochemical Properties

In this study a cationic surfactant, cetyltrimethylammonium bromide (CTAB), was used as a soft template for in situ chemical polymerization of aniline on the surface of microcrystalline cellulose (MCC). The morphology of the wire-like and porous nanostructure of the resulting composite was highly dependent on the MCC and CTAB concentrations. The effect of the MCC and CTAB concentrations on the electrochemical and morphological properties of the polyaniline (PAni) nanocomposite was studied. Cyclic voltammograms of modified PAni/MCC/CTAB electrode displayed a high current response and the effect of scan rate on the current response confirmed a diffusion controlled process on the surface of the electrode that makes it suitable for sensor applications. The overlapping characteristic peaks of pure PAni and MCC caused peak broadening at 3263 cm^-1 in the IR spectra of PAni/MCC/CTAB nanocomposite that revealed the interaction between NH of PAni and OH group of MCC via electrostatic interactions. The addition of MCC to PAni through chemical polymerization decreased the thermal stability of composite compared to pure PAni. Lower crystallinity was observed in the XRD diffractogram, with 2 theta values of 22.8, 16.5, and 34.6 for PAni/MCC, confirming the formation of PAni on the MCC surface.

Fluorescent DNA Probing Nanoscale MnO2: Adsorption, Dissolution by Thiol, and Nanozyme Activity

Manganese dioxide (MnO₂) is an interesting material due to its excellent biocompatibility and magnetic properties. Adsorption of DNA to MnO₂ is potentially of interest for drug delivery and sensing applications. However, little fundamental understanding is known about their interactions. In this work, carboxyfluorescein (FAM)-labeled DNA oligonucleotides were used to explore the effect of salt concentration, pH, and DNA sequence and length for adsorption by MnO₂, and comparisons were made with graphene oxide (GO). The DNA desorbs from MnO₂ by free inorganic phosphate, while it desorbs from GO by adenosine and urea. Therefore, DNA is mainly adsorbed on MnO₂ through its phosphate backbone, and DNA has a stronger affinity on MnO₂ than on GO based on a salt-shock assay. At the same time, DNA was used to study the effect of thiol containing compounds on the dissolution of MnO₂. Adsorbed DNA was released from MnO₂ after its dissolution by thiol, but not from other metal oxides with lower solubility such as CeO₂, TiO₂, and Fe₃O₄. DNA-functionalized MnO₂ was then used for detecting glutathione (GSH) with a detection limit of 383 nM. Finally, DNA was found to inhibit the peroxidase-like activity of MnO₂. This study has offered many fundamental insights into the interaction between MnO₂ and two important biomolecules: DNA and thiol-containing compounds.

DNA metallization: principles, methods, structures, and applications

This review summarizes the research activities on DNA metallization since the concept was first proposed in 1998, covering the principles, methods, structures, and applications.

Microwave assisted fast formation of Sn(MoO4)2 nano-assemblies on DNA scaffold for application in lithium-ion batteries

Self-assembled aggregated Sn(MoO₄)₂ nanomaterials on DNA scaffolds exhibit enhanced capability as anode materials in lithium-ion battery (LIB) applications.

Methods and strategies for the synthesis of diverse nanoparticles and their applications: a comprehensive overview

Various methods to synthesize diverse nanoparticles with their different applications.