Carbon-dot-triggered aggregation/dispersion of gold nanoparticles for colorimetric detection of nucleic acids and its application in visualization of loop-mediated isothermal amplification

In this study, cationic carbon dots (CDs) were prepared from p-phenylenediamine (pPDA) via a one-step hydrothermal method and used to trigger the aggregation and dispersion of gold nanoparticles (AuNPs) for the colorimetric detection of nucleic acids. Physicochemical characterization results revealed that the CDs are enriched with positively charged surface functional groups with an average size of ∼11 nm. The interaction between the CDs and AuNPs was confirmed via fluorescence and absorption studies. Absorption spectroscopic results revealed that the primary surface plasmon resonance (SPR) band of the AuNPs decreased upon introduction of CDs, and a new band emerged at ∼600 nm, indicating the aggregated assembly of AuNPs. Upon the introduction of double-stranded deoxyribonucleic acid (DNA), the band corresponding to the aggregated AuNPs showed a continuous decrease, accompanied by a simultaneous increase in the primary SPR band, leading to a noticeable purple-to-red color transformation. Based on this phenomenon, a colorimetric assay for DNA was developed, which relies on the interaction between negatively charged DNA and cationic CDs, leaving the AuNPs dispersed. The assay exhibited a linear response within a DNA concentration range of 0.7-14 nM with a detection limit of 1.70 nM. Selectivity results showed that colorimetric assays are specific for both DNA and single-stranded DNA (ssDNA). Smartphone-assisted detection was developed by monitoring the colorimetric response of a AuNPs/CDs probe. As a proof-of-concept experiment, the AuNPs/CDs probe was used to visualize the loop-mediated isothermal amplification (LAMP) of Escherichia coli (E. coli), a robust indicator of sewage contamination in water.

A magnetic field augmented ultra-thin layer chromatography coupled surface enhanced Raman spectroscopy separation of hemozoin from bacterial mixture

Malaria is considered as one the most widespread disease with highest possibility of co-infection at all levels of the disease prognosis. Rapid detection and discrimination of malaria from other co-infections remains a challenge. Hemozoin is a metabolic biproduct of malaraia possessing paramagnetic property due to presence of iron at its centre. Here, we report a label free, rapid and highly sensitive magnetic field based ultra-thin layer chromatography (UTLC) coupled with surface enhanced Raman spectroscopy (SERS) technique for detection and separation of hemozoin from a bacterial mixture. Highly optimized silver nanorods chip fabricated using glancing angle deposition (GLAD) is explored for the UTLC-SERS separation. These chips possessing channel like characteristic and high surface to the volume ratio serve as excellent UTLC plates. The magnetic nature of hemozoin has been exploited for its separation from the mixture of P. aeruginosa (Gram-negative) and S. aureus (Gram-positive) by allocating a 0.6 T magnet over the UTLC flow setup. The solvent front migrated approximately to a distance of 13 mm from the sample point due to the magnetic environment. Spatially resolved SERS data was collected along the mobile phase and separation of mixture was confirmed. Further, staining of hemozoin, P. aeruginosa and S. aureus was done using methylene blue, acridine orange and rhodamine 6 G respectively. The separation was confirmed for the stained analytes. The present developed method provides plate height as low as 18 µm and hemozoin detection limit as <10 parasites/mL. Therefore, we establish a highly specific and sensitive technique capable of separating small amounts of bioanalytes, aiding in the removal of co-infections from the disease at a very early stage of infection.

Watermelon rinds as cost-efficient adsorbent for acridine orange: a response surface methodological approach

In the current investigation, watermelon rinds (WMR) have been utilized as an eco-friendly and cost-efficient adsorbent for acridine orange (AO) from contaminated water samples. Adsorption of AO onto raw (RWM) and thermally treated rinds (TTWM250 and TTWM500) has been studied. The adsorption efficiency of the three adsorbents was evaluated by measuring the % removal (%R) of AO and the adsorption capacity (q_e, mg/g). Dependent variables (%R and q_e) were optimized as a function of four factors: pH, sorbent dosage (AD), the concentration of AO (DC), and contact time (ST). Box-Behnken (BB) design has been utilized to obtain the optimum adsorption conditions. Prepared adsorbents have been characterized using scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR), and Raman spectroscopies. The surface area of RWM, TTWM250, and TTWM500, as per the Brunauer-Emmett-Teller (BET) analysis, was 2.66, 2.93, and 5.03 m²/g, respectively. Equilibrium investigations suggest that Freundlich model was perfectly fit for adsorption of AO onto TTWM500. Maximum adsorption capacity (q_max) of 69.44 mg/g was obtained using the Langmuir equation. Adsorption kinetics could be best described by the pseudo-second-order (PSO) model. The multi-cycle sorption-desorption study showed that TTWM500 could be regenerated with the adsorption efficiency being preserved up to 87% after six cycles.

Toxicity of silver nanoparticles on different tissues in adult Danio rerio

Although silver nanoparticles (AgNP) are among the most studied nanomaterials by virtue of their broad application in many areas, little is known about their overall toxicity to aquatic organisms after their contamination of the water environment. This study aimed to analyze the effect of the exposure (96 h) to different AgNP concentrations on Danio rerio (zebrafish) tissues. AgNP were synthesized and characterized by transmission electron microscopy (TEM), showing spherical AgNP of 30.00 ± 16.80 nm size. The effects of different AgNP concentrations (1, 3, and 5 μg L^-1) on brain, muscle, gill, and liver tissues of zebrafish were investigated. The results show a significant decrease in brain and muscle acetylcholinesterase (AChE) activity. Liver and gill catalase (CAT) activity also decreased significantly. At the highest exposure concentration, muscle AChE was more inhibited (37.3%) than brain AChE (26.4%) and gill CAT was more inhibited (67.4%) than liver CAT (51.2%). D. rerio also showed gill morphological changes such as fusion of secondary lamellae, curvature, dilated marginal channel, and epithelial lifting. This study indicates that gill CAT together with morphological studies are potential biomarkers for AgNP.

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.

Understanding the effect of size and shape of gold nanomaterials on nanometal surface energy transfer

Gold Nanomaterials (GNMs) interact with fluorophores via electromagnetic coupling under excitation. In this particular work we carried out (to the best of our knowledge for the first time) a comprehensive study of systematic quenching of a blue emitter 2-Anthracene Sulfonate (2-AS) in the presence of gold nanoparticles of different size and shape. We synthesized gold nanomaterials of four different dimensions [nanoparticle (0D), nanorod (1D), nanotriangle (2D) and nanobipyramids (3D)] and realized the underlying effect on the emitting dipole in terms of steady and time resolved fluorescence. Nanometal Surface Energy Transfer (NSET) has already been proved to be the best long range spectroscopic ruler so far. Many attempts have been made to understand the interaction between a fluorescent molecule and gold nanomaterials. But not a single model can interpret alone the interaction phenomena. We have opted three different models to compare the experimental and theoretical data. Due to the presence of size dependent absorptivity and dielectric function, modified CPS-Kuhn model was proved to be the worthiest to comprehend variance of behavior of an emitting dipole in close proximity to nanometal surface by coupling with the image dipole of gold nanomaterials.