Signal amplification of SiO2 nanoparticle loaded horseradish peroxidase for colorimetric detection of lead ions in water

A novel dual-mode aptasensor based on a multiple amplification system for ultrasensitive detection of lead ions using fluorescence and surface-enhanced Raman spectroscopy

In this work, we develop a dual recycling amplification aptasensor for sensitive and rapid detection of lead ions (Pb2+) using fluorescence and surface-enhanced Raman scattering (FL-SERS). The aptasensor allows targeted cleavage of substrates through specifically binding with the Pb2+-dependent aptamer (M-PS2.M). Ultrasensitive detection of trace Pb2+ has been achieved using an enzyme-free nonlinear hybridization chain reaction (HCR) and the FL-SERS technique. The lower limit of detection (LOD = 3σ/k) is 0.115 pM in FL mode and 1.261 fM in SERS mode. The aptasensor is characterized by high reliability and specificity, among other things, to distinguish Pb2+ from other metal ions. In addition, the aptasensor can detect Pb2+ in actual water with good recovery. Compared with the single-mode aptasensor, the dual-mode aptasensor is characterized by high reliability, an extensive detection range, and high specificity.

Nanomaterials-based aptasensors: An efficient detection tool for heavy-metal and metalloid ions in environmental and biological samples

In light of potential risks of heavy metal exposure, diverse aptasensors have been developed through the combination of aptamers with nanomaterials for the timely and efficient detection of metals in environmental and biological matrices. Aptamer-based sensors can benefit from multiple merits such as heightened sensitivity, facile production, uncomplicated operation, exceptional specificity, enhanced stability, low immunogenicity, and cost-effectiveness. This review highlights the detection capabilities of nanomaterial-based aptasensors for heavy-metal and metalloid ions based on their performance in terms of the basic quality assurance parameters (e.g., limit of detection, linear dynamic range, and response time). Out of covered studies, dendrimer/CdTe@CdS QDs-based ECL aptasensor was found as the most sensitive option with an LOD of 2.0 aM (atto-molar: 10-18 M) detection for Hg2+. The existing challenges in the nanomaterial-based aptasensors and their scientific solutions are also discussed.

Advances in colorimetric aptasensors for heavy metal ion detection utilizing nanomaterials: a comprehensive review

Heavy metal ion contamination poses significant environmental and health risks, necessitating rapid and efficient detection methods. In the last decade, colorimetric aptasensors have emerged as powerful tools for heavy metal ion detection, owing to their notable attributes such as high specificity, facile synthesis, adaptability to modifications, long-term stability, and heightened sensitivity. This comprehensive overview summarizes the key developments in this field over the past ten years. It discusses the principles, design strategies, and innovative techniques employed in colorimetric aptasensors using nanomaterials. Recent advancements in enhancing sensitivity, selectivity, and on-site applicability are highlighted. The review also presents application studies of successful heavy metal ion detection using colorimetric aptasensors, underlining their potential for environmental monitoring and health protection. Finally, future directions and challenges in the continued evolution of these aptasensors are outlined.

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 Label-Free Optical Detection of Pb2+ Ions via Colloidal Gold Nanoparticles

The detection of the lead heavy metal (Pb) in water is crucial in many chemical processes, as it is associated with serious health hazards. Here, we report the selective and precise colorimetric detection of Pb2+ ions in water, exploiting the aggregation and self-assembly mechanisms of glutathione (GSH)-functionalized gold nanoparticles (GNPs). The carboxyl functional groups are able to create coordination complexes with Pb2+, inducing aggregation amongst the GSH-GNPs in the presence of Pb2+ due to the chelation of the GSH ligands. The resulting aggregation amongst the GSH-GNPs in the presence of Pb2+ increases the aggregate size depending on the available Pb2+ ions, affecting the plasmonic coupling. This causes a substantial shift in the plasmon wavelength to a longer wavelength side with increasing Pb2+ concentration, resulting in a red-to-blue colorimetric or visual change, enabling the instant determination of lead content in water.

The Effect of a Rotating Cone on Horseradish Peroxidase Aggregation on Mica Revealed by Atomic Force Microscopy

Our study reported herein aims to determine whether an electromagnetic field, induced triboelectrically by a metallic cone, rotating at a frequency of 167 Hz, has an effect on the properties of the horseradish peroxidase (HRP) enzyme. Atomic force microscopy (AFM) was employed to detect even the most subtle effects on single enzyme molecules. In parallel, a macroscopic method (spectrophotometry) was used to reveal whether the enzymatic activity of HRP in solution was affected. An aqueous solution of the enzyme was incubated at a distance of 2 cm from the rotating cone. The experiments were performed at various incubation times. The control experiments were performed with a non-rotating cone. The incubation of the HRP solution was found to cause the disaggregation of the enzyme. At longer incubation times, this disaggregation was found to be accompanied by the formation of higher-order aggregates; however, no change in the HRP enzymatic activity was observed. The results of our experiments could be of interest in the development of enzyme-based biosensors with rotating elements such as stirrers. Additionally, the results obtained herein are important for the correct interpretation of data obtained with such biosensors.

Atomic Force Microscopy Study of the Temperature and Storage Duration Dependencies of Horseradish Peroxidase Oligomeric State

This paper presents an investigation of the temperature dependence of the oligomeric state of the horseradish peroxidase (HRP) enzyme on the temperature of its solution, and on the solution storage time, at the single-molecule level. Atomic force microscopy has been employed to determine how the temperature and the storage time of the HRP solution influence its aggregation upon direct adsorption of the enzyme from the solution onto bare mica substrates. In parallel, spectrophotometric measurements have been performed in order to estimate whether the HRP enzymatic activity changes over time upon the storage of the enzyme solution. The temperature dependence of the HRP oligomeric state has been studied within a broad (15–40 °C) temperature range. It has been demonstrated that the storage of the HRP solution for 14 days does not have any considerable effect on the oligomeric state of the enzyme, neither does it affect its activity. At longer storage times, AFM has allowed us to reveal a tendency of HRP to oligomerization during the storage of its buffered solution, while the enzymatic activity remains virtually unchanged even after a 1-month-long storage. By AFM, it has been revealed that after the incubation of a mica substrate in the HRP solution at various temperatures, the content of the mica-adsorbed oligomers increases insignificantly owing to a high-temperature stability of the enzyme.

The Effect of Incubation near an Inversely Oriented Square Pyramidal Structure on Adsorption Properties of Horseradish Peroxidase

The incubation of a solution of horseradish peroxidase (HRP) enzyme either below the apex or near the base of an inversely oriented square pyramid (inverted square pyramid; ISP) has been found to influence the enzyme’s aggregation and adsorption properties. The HRP enzyme is used herein as a model object due to its importance in analytical chemistry applications. Atomic force microscopy (AFM) is employed to investigate the HRP’s adsorption on mica substrates at the single-molecule level. Conventional spectrophotometry is used in parallel as a reference method for the determination of the HRP’s enzymatic activity. Using AFM, we reveal a significant change in the adsorption properties of HRP on mica substrates after the incubation of the HRP solutions either above the base or below the apex of the ISP in comparison with the control HRP solution. The same situation is observed after the incubation of the enzyme solution above the center of the ISP’s base. Here, the enzymatic activity of HRP remained unaffected in both cases. Since pyramidal structures of positive and inverted orientation are employed in biosensor devices, it is important to take into account the results obtained herein in the development of highly sensitive biosensor systems, in which pyramidal structures are employed as sensor (such as AFM probes) or construction elements.