Comprehensive review on fluorescent carbon dots and their applications in nucleic acid detection, nucleolus targeted imaging and gene delivery.

Carbon dots (CDs), including carbon quantum dots, graphene quantum dots, carbon nanodots, and polymer dots, have gained significant attention due to their unique structural and fluorescence characteristics. This review provides a comprehensive overview of the classification, structural characteristics, and fluorescence properties of CDs, followed by an exploration of various fluorescence sensing mechanisms and their applications in gene detection, nucleolus imaging, and gene delivery. Furthermore, the functionalization of CDs with diverse surface ligand molecules, including dye molecules, nucleic acid probes, and metal derivatives, for sensitive nucleic acid detection is systematically examined. Fluorescence imaging of the cell nucleolus plays a vital role in examining intracellular processes and the dynamics of subcellular structures. By analyzing the mechanism of fluorescence and structure-function relationships inherent in CDs, the nucleolus targeting abilities of CDs in various cell lines have been discussed. Additionally, challenges such as the insufficient organelle specificity of CDs and the inconsistent mechanisms underlying nucleolus targeting have also been highlighted. The unique physical and chemical properties of CDs, particularly their strong affinity toward deoxyribonucleic acid (DNA), have spurred interest in gene delivery applications. The use of nuclear-targeting peptides, polymers, and ligands in conjunction with CDs for improved gene delivery applications have been systematically reviewed. Through a comprehensive analysis, the review aims to contribute to a deeper understanding of the potential and challenges associated with CDs in biomedical applications.

Dual-Emissive Carbon Dots: Exploring Their Fluorescence Properties for Sensitive Turn-Off-On Recognition of Ferric and Pyrophosphate Ions and Its Application in Fluorometric Detection of the Loop-Mediated Isothermal Amplification Reaction.

In this study, dual-emissive carbon dots (CDs) were prepared using p-phenylenediamine (pPDA) and phytic acid (PA) precursors via a one-pot-hydrothermal method. The photophysical, morphological, and structural characterization of CDs was carried out using absorption, fluorescence, Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR), and high-resolution transmission electron microscopy (HR-TEM) analysis. The as-prepared CDs displayed dual-fluorescence peaks at 525 and 620 nm upon excitation at 450 nm. The CDs showed good photostability and exhibited solvent-dependent fluorescence properties. The solvatochromic behavior of CDs was utilized to detect water content in organic solvents. Furthermore, the dual-emissive property of CDs was utilized for the sequential detection of ferric (Fe3+) and pyrophosphate ions (PPi) by a fluorescence turn-off-on mechanism. The proposed assay showed appreciable fluorescence response toward Fe3+ and PPi with high selectivity and good tolerance for common interfering ions. The potential practical application of the CD probe was ascertained by carrying out the fluorometric detection of PPi to affirm the loop-mediated isothermal amplification (LAMP) reaction specific for Mycobacterium tuberculosis (negative and positive clinical samples).

A review of biomolecules conjugated lanthanide up-conversion nanoparticles-based fluorescence probes in food safety and quality monitoring applications.

Upconversion nanoparticles (UCNPs) are known to possess unique characteristics, which allow them to overcome a number of issues that plague traditional fluorescence probes. UCNPs have been employed in a variety of applications, but it is arguably in the realm of optical sensors where they have shown the most promise. Biomolecule conjugated UCNPs-based fluorescence probes have been developed to detect and quantify a wide range of analytes, from metal ions to biomolecules, with great specificity and sensitivity. In this review, we have given much emphasis on the recent trends and progress in the preparation strategies of bioconjugated UCNPs and their potential application as fluorescence sensors in the trace level detection of food industry-based toxicants and adulterants. The paper discusses the preparation and functionalisation strategies of commonly used biomolecules over the surface of UCNPs. The use of different sensing strategies namely heterogenous and homogenous assays, underlying fluorescence mechanisms in the detection process of food adulterants are summarized in detail. This review might set a precedent for future multidisciplinary research including the development of novel biomolecules conjugated UCNPs for potential applications in food science and technology.

Elucidation of photophysical changes and orientation of acridine orange dye on the surface of borate capped gold nanoparticles using multi-spectroscopic techniques.

In the present work, we have carried out a detailed investigation on the binding interaction of acridine orange (AO) with borate capped gold nanoparticles (Au NPs) by absorption spectroscopy, steady state emission spectroscopy, time resolved fluorescence spectroscopy, high resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS), zeta potential measurements, Fourier transform infrared (FT-IR) and Raman spectroscopy. The phenomena of hypochromism and the appearance of coupled localized surface plasmon resonance (LSPR) bands in the absorption spectral studies of the AO-Au NP system suggested the vital role of electrostatic interactions between AO dye and Au NPs. The results from HR-TEM and DLS measurements confirmed the formation of aggregated clusters of nanoparticles. The zeta potential studies of Au NPs and AO coated Au NPs suggested the occurrence of partial surface charge neutralization of negatively charged Au NPs by cationic AO dye. The interparticle edge to edge separation distance of adjacent Au NPs revealed the presence of AO molecules between the nano-gaps of Au NPs. Emission spectral studies of AO in the presence of increasing concentrations of Au NPs indicated the existence of a static quenching mechanism. Time resolved fluorescence spectroscopic study further validated the findings of steady state emission measurements. The comparison of experimental emission quenching data with the theoretically calculated value suggested the probable multi-layered assembly of AO on the surface of Au NPs. FT-IR and Raman spectral studies further revealed the existence of electrostatic interactions and possible horizontal orientation of AO dye molecules on Au NP surfaces.

New insights into the photophysical properties and interaction mechanisms of Janus green blue dye with polyanions and its applications in colorimetric visualization of loop-mediated isothermal amplification and polymerase chain reaction.

In this investigation, the photophysical properties and interaction mechanisms of Janus green blue (JGB) dye with polyanions were systematically studied using spectroscopic techniques. The absorption spectral analysis revealed that JGB binds cooperatively to sodium alginate, leading to dye stacking along the polymer chain. The interaction of JGB dye with DNA was characterized by the emergence of a metachromatic peak at 564 nm, indicating the formation of dye aggregates. The analysis of absorption data reveals that JGB dye interacts with DNA at multiple binding sites, including at least one high-affinity site. The AutoDock Vina based blind docking approach was used to analyze the most probable binding location of JGB dye in DNA. By making use of the DNA-induced metachromasia, a colorimetric approach was developed for the visualization of loop-mediated isothermal amplification (LAMP) and polymerase chain reaction (PCR). The LAMP-colorimetric assay, targeting the Streptococcus pneumoniae gene, demonstrated a noticeable colour change with a detection limit of 1 pg µL-1. The practical applicability was validated by detecting S. pneumoniae in artificial urine. In addition to LAMP, we tested the JGB dye based colorimetric assay for applicability in PCR reactions. The colorimetric PCR assay using the metal-responsive transcription factor (MTF-1) gene achieved a detection limit as low as 0.1 pg µL-1. The study highlights the potential of DNA binding metachromic dye to significantly enhance colorimetric assays, offering a robust and sensitive tool for molecular diagnostics.

New insights into the binding interaction of food protein ovalbumin with malachite green dye by hybrid spectroscopic and molecular docking analysis.

Communicated by Ramaswamy H. Sarma.

Carbon Quantum Dot-Anchored Bismuth Oxide Composites as Potential Electrode for Lithium-Ion Battery and Supercapacitor Applications.

The present investigation elucidates a simple hydrothermal method for preparing nanostructured bismuth oxide (Bi2O3) and carbon quantum dot (CQD) composite using spoiled (denatured) milk-derived CQDs. The formation of the CQD-Bi2O3 composite was confirmed by UV-vis absorption, steady-state emission, and time-resolved fluorescence spectroscopy studies. The crystal structure and chemical composition of the composite were examined by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The surface morphology and the particle size distribution of the CQD-Bi2O3 were examined using field emission scanning electron microscope and high-resolution transmission electron microscope observations. As an anode material in lithium-ion battery, the CQD-Bi2O3 composite exhibited good electrochemical activity and delivered a discharge capacity as high as 1500 mA h g-1 at 0.2C rate. The supercapacitor properties of the CQD-Bi2O3 composite electrode revealed good reversibility and a high specific capacity of 343 C g-1 at 0.5 A g-1 in 3 M KOH. The asymmetric device constructed using the CQD-Bi2O3 and reduced graphene oxide delivered a maximum energy density of 88 Wh kg-1 at a power density of 2799 W kg-1, while the power density reached a highest value of 8400 W kg-1 at the energy density of 32 Wh kg-1. The practical viability of the fabricated device is demonstrated by glowing light-emitting diodes. It is inferred that the presence of conductive carbon network has significantly increased the conductivity of the oxide matrix, thereby reducing the interfacial resistance that resulted in excellent electrochemical performances.

Comprehensive Multispectroscopic Analysis on the Interaction and Corona Formation of Human Serum Albumin with Gold/Silver Alloy Nanoparticles.

In the present investigation, we have systematically studied the binding mechanism of model protein human serum albumin (HSA) with gold/silver alloy nanoparticles (Au/Ag NPs) using multiple spectroscopic techniques. Absorption spectral studies of Au/Ag NPs in the presence of increasing concentrations of HSA resulted in a slight red shift of the surface plasmon resonance band (SPR) of Au/Ag NPs, suggesting changes in the refractive index around the nanoparticle surface owing to the adsorption of HSA. The results from high-resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS), and zeta potential analysis substantiated the formation of a dense layer of HSA on the surface of Au/Ag NPs. The formation of a ground-state complex between HSA and Au/Ag NPs was evident from the outcome of the steady-state emission titration experiments of the HSA-Au/Ag NPs system. The binding parameters computed from corrected emission quenching data revealed that HSA exhibited a significant binding affinity toward Au/Ag NPs. The identical fluorescence lifetime values of HSA and HSA-Au/Ag NPs from time-resolved fluorescence spectroscopic analysis further authenticated the findings of steady-state emission measurements. The formation of HSA corona on the Au/Ag NPs surface was established on the basis of experimental quenching data and theoretical values. The occurrence of partial unfolding of HSA upon its interaction with the Au/Ag NPs surface was established by using an extrinsic fluorophore 1-anilino-8-naphthalenesulfonic acid (ANS). Absorption, Fourier transform infrared (FT-IR), Raman, circular dichroism (CD), and excitation-emission matrix (3D) spectral studies were also carried out to explore Au/Ag NPs-induced tertiary and secondary conformational changes of HSA. The influence of Au/Ag NPs on the esterase-like activity of HSA was established by probing the hydrolysis of p-nitrophenyl acetate.