Green synthesis, characterization of Radix Hedysari-mediated silver nanoparticles and their use for sensitive colorimetric detection of Pb2+ in the Yellow River medium

Aggregation-induced enhancement of peroxidase-mimetic activity of DNAzyme-gold nanoparticles for ultrasensitive detection of lead ions

Lead ion (Pb2+) detection is critically important in environmental protection and health management. In this work, we developed a simple signal-enhanced colorimetric sensor for the detection of Pb2+ based on the peroxidase-mimetic property of gold nanoparticles (AuNPs). When a certain concentration of Pb2+ was added to a solution of DNAzyme-modified AuNPs, aggregation was triggered, and the result was an enhancement of the peroxidase-mimetic activity of AuNPs. Then, the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB) by the catalyst of AuNPs was used for the sensitive UV-Vis and colorimetric detection of Pb2+. When a higher concentration of Pb2+ was added, the greater amount of aggregation of AuNPs resulted in the enhancement of the UV-Vis adsorption of the solution at 652 nm, with a deepening of the blue color of the solution. After optimization of the experimental conditions, a linear relationship between the absorbance of oxidized TMB at 652 nm and the logarithm of Pb2+ concentration was obtained, which had been divided into two parts (25 pM to 2.5 μM, and 2.5 μM to 250 μM). The detection limit was as low as 10 pM. The satisfactory specificity and rapid response of the sensor showed that it has promising application for the detection of Pb2+ in real samples.

Colorimetric and naked-eye detection of arsenic(iii) using a paper-based microfluidic device decorated with silver nanoparticles

Arsenic (As) as a metal ion has long-term toxicity and its presence in water poses a serious threat to the environment and human health. So, rapid and accurate recognition of traces of As is of particular importance in environmental and natural resources. In this study, a fast and sensitive colorimetric method was developed using silver nano prisms (Ag NPrs), cysteine-capped Ag NPrs, and methionine-capped Ag NPrs for accurate detection of arsenic-based on transforming the morphology of silver nanoparticles (AgNPs). The generated Ag atoms from the redox reaction of silver nitrate and As(iii) were deposited on the surface of Ag NPrs and their morphology changed to a circle. The morphological changes resulted in a change in the color of the nanoparticles from blue to purple, which was detectable by the naked eye. The rate of change was proportional to the concentration of arsenic. The changes were also confirmed using UV-Vis absorption spectra and showed a linear relationship between the change in adsorption peak and the concentration of arsenic in the range of 0.0005 to 1 ppm with a lower limit of quantification (LLOQ) of 0.0005 ppm. The proposed probes were successfully used to determine the amount of As(iii) in human urine samples. In addition, modified microfluidic substrates were fabricated with Ag NPrs, Cys-capped Ag NPrs, and methionine-capped Ag NPrs nanoparticles that are capable of arsenic detection in the long-time and can be used in the development of on-site As(iii) detection kits. In addition, silver nanowires (AgNWs) were used as a probe to detect arsenic, but good results were not obtained in human urine specimens and paper microfluidic platforms. In this study, for the first time, AgNPs were developed for optical colorimetric detection of arsenic using paper-based microfluidics. Ag NPrs performed best in both optical and colorimetric techniques. Therefore, they can be a promising option for the development of sensitive, inexpensive, and portable tools in the environmental and biomedical diagnosis of As(iii).

Natural and Engineered Nanomaterials for the Identification of Heavy Metal Ions—A Review

In recent years, there has been much interest in developing advanced and innovative approaches for sensing applications in various fields, including agriculture and environmental remediation. The development of novel sensors for detecting heavy metals using nanomaterials has emerged as a rapidly developing research area due to its high availability and sustainability. This review emphasized the naturally derived and engineered nanomaterials that have the potential to be applied as sensing reagents to interact with metal ions or as reducing and stabilizing agents to synthesize metallic nanoparticles for the detection of heavy metal ions. This review also focused on the recent advancement of nanotechnology-based detection methods using naturally derived and engineered materials, with a summary of their sensitivity and selectivity towards heavy metals. This review paper covers the pros and cons of sensing applications with recent research published from 2015 to 2022.