Graphene and AuNPs based electrochemical aptasensor for ultrasensitive detection of hydroxylated polychlorinated biphenyl

Advancements in nanomaterial-based aptasensors for the detection of emerging organic pollutants in environmental and biological samples

The combination of nanomaterials (NMs) and aptamers into aptasensors enables highly specific and sensitive detection of diverse pollutants. The great potential of aptasensors is recognized for the detection of diverse emerging organic pollutants (EOPs) in different environmental and biological matrices. In addition to high sensitivity and selectivity, NM-based aptasensors have many other advantages such as portability, miniaturization, facile use, and affordability. This work showcases the recent advances achieved in the design and fabrication of NM-based aptasensors for monitoring EOPs (e.g., hormones, phenolic contaminants, pesticides, and pharmaceuticals). On the basis of their sensing mechanisms, the covered aptasensing systems are classified as electrochemical, colorimetric, PEC, fluorescence, SERS, and ECL. Special attention has been paid to the fabrication processes, analytical achievements, and sensing mechanisms of NM-based aptasensors. Further, the practical utility of aptasensing approaches has also been assessed based on their basic performance metrics (e.g., detection limits, sensing ranges, and response times).

Graphene Based Nanohybrid Aptasensors in Environmental Monitoring: Concepts, Design and Future Outlook

In view of ever-increasing environmental pollution, there is an immediate requirement to promote cheap, multiplexed, sensitive and fast biosensing systems to monitor these pollutants or contaminants. Aptamers have shown numerous advantages in being used as molecular recognition elements in various biosensing devices. Graphene and graphene-based materials/nanohybrids combined with several detection methods exhibit great potential owing to their exceptional optical, electronic and physicochemical properties which can be employed extensively to monitor environmental contaminants. For environmental monitoring applications, aptamers have been successfully combined with graphene-based nanohybrids to produce a wide range of innovative methodologies. Aptamers are immobilized at the surface of graphene based nanohybrids via covalent and non-covalent strategies. This review highlights the design, working principle, recent developmental advances and applications of graphene based nanohybrid aptasensors (GNH-Apts) (since January 2014 to September 2021) with a special emphasis on two major signal-transduction methods, i.e., optical and electrochemical for the monitoring of pesticides, heavy metals, bacteria, antibiotics, and organic compounds from different environmental samples (e.g., water, soil and related). Lastly, the challenges confronted by scientists and the possible future outlook have also been addressed. It is expected that high-performance graphene-based nanohybrid aptasensors would find broad applications in the field of environmental monitoring.

An electrochemical aptasensor-based CoxP-decorated porous carbon microspheres and AuNRs labelled methylene blue as signal labels for the sensitive detection of PCB77

In this work, a simple, specific and ultra-sensitive electrochemical aptasensor was successfully developed based on a novel signal reduction strategy for the detection of polychlorinated biphenyls (PCB77). This aptasensor was prepared by the electrodeposition of gold nanoparticles (AuNPs) on an Au electrode (AuE) modified with cobalt phosphide (Co_xP, a mixture of CoP and Co₂P) decorated porous carbon microspheres. In this study, the thiolated single-complementary DNA (cDNA) was immobilized on the surface of the modified electrode via the Au-S bond. Subsequently, the gold nanorod@methylene blue connection aptamer (AuNRs@MB-Apt) signal labels were immobilized onto the modified electrode through the principle of complementary base pairing. Further, the aptamer preferentially binds to PCB77, decreasing the amount of AuNR@MB-Apt. The DPV current response was related to the PCB77 concentration. Under the optimized experimental conditions, a low detection limit of 5.9 × 10^-2 ng L^-1 and a wide linear range of 1 × 10^-11 mg mL^-1 to 1 × 10^-4 mg mL^-1 (S/N = 3) for PCB77 were achieved. Moreover, the proposed aptasensor offered high selectivity, stability and reproducibility, indicating the broad potential application in environmental monitoring.

Aptamer-Based Biosensors for Environmental Monitoring

Due to their relative synthetic and chemical simplicity compared to antibodies, aptamers afford enhanced stability and functionality for the detection of environmental contaminants and for use in environmental monitoring. Furthermore, nucleic acid aptamers can be selected for toxic targets which may prove difficult for antibody development. Of particular relevance, aptamers have been selected and used to develop biosensors for environmental contaminants such as heavy metals, small-molecule agricultural toxins, and water-borne bacterial pathogens. This review will focus on recent aptamer-based developments for the detection of diverse environmental contaminants. Within this domain, aptamers have been combined with other technologies to develop biosensors with various signal outputs. The goal of much of this work is to develop cost-effective, user-friendly detection methods that can complement or replace traditional environmental monitoring strategies. This review will highlight recent examples in this area. Additionally, with innovative developments such as wearable devices, sentinel materials, and lab-on-a-chip designs, there exists significant potential for the development of multifunctional aptamer-based biosensors for environmental monitoring. Examples of these technologies will also be highlighted. Finally, a critical perspective on the field, and thoughts on future research directions will be offered.

Ultrasensitive voltammetric and impedimetric aptasensor for diazinon pesticide detection by VS2 quantum dots-graphene nanoplatelets/carboxylated multiwalled carbon nanotubes as a new group nanocomposite for signal enrichment

Polluted water and groundwater resources contaminated by pesticides are among the most important environmental distresses. Therefore, a simple, ultrasensitive, and selective electrochemical aptasensor is proposed for diazinon (DZN) determination as an organophosphorus compound. The vanadium disulfide quantum dots (VS₂QDs) were synthesized by a facile hydrothermal method and doped on the graphene nanoplatelets/carboxylated multiwalled carbon nanotubes (GNP/CMWCNTs) as a new group of nanocomposite. The prepared nanocomposite (VS₂QDs-GNP/CMWCNTs) on a glassy carbon electrode (GCE) was incubated with the DZN binding aptamer (DZBA) through electrostatic interaction (GCE/VS₂QDs-GNP/CMWCNTs/DZBA). The modified electrode was used for the low detection of DZN by monitoring the oxidation of [Fe(CN)6]^3-/4- as the redox probe. The characterizations of the modified electrode were performed by several electrochemical methods include: cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Also, the prepared nanocomposite was characterized with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV-Vis absorption spectroscopy, fourier transform infrared (FT-IR), fluorescence emission spectroscopy, dynamic light scattering (DLS), elemental mapping, and energy dispersive spectroscopy (EDS). The DZBA selectively adsorbs DZN on the modified electrode, leading to a decrease and increase in the current of DPV and charge transfer resistance (R_CT) of EIS, respectively, as analytical signals. The developed electrochemical aptasensor at the optimal conditions have low limits of detection (LOD) equal to 1.1 × 10^-14 and 2.0 × 10^-15 mol L^-1 with wide dynamic ranges of 5.0 × 10^-14-1.0 × 10^-8 mol L^-1 and 1.0 × 10^-14-1.0 × 10^-8 mol L^-1 for DPV and EIS calibration curves, respectively. Finally, this aptasensor had good selectivity, stability, reproducibility, and feasibility for the DZN detection in various real samples.

New trends in the electrochemical detection of endocrine disruptors in complex media

Endocrine disruptors (EDCs) are substances existing in the environment which affect animal and human endocrine functions and cause diseases. A small quantity of EDCs can have a serious impact on the body. Currently, enzyme-linked immunosorbent assay (ELISA), high-performance liquid chromatography (HPLC), and other traditional methods are used to detect EDCs. Although their sensitivity and reliability are good, these methods are complex, expensive, and not feasible to use in the field. Electrochemical techniques present good potential for the detection of EDCs owing to their low cost, simple, and wearable instrumentation. This paper presents the new trends in this field over the last 3 years. Some simple materials can allow some EDCs to be directly detected. New designs of biosensors, such as aptasensors, allow a femtomolar limit of detection to be reached. Many types of nanomaterial-based sensors were tested; carbonaceous nanomaterials, such as multiwalled carbon nanotubes (MWCNTs) and reduced graphene oxide (rGO), associated or not with other types of nanoparticles were included in numerous designs. Molecularly imprinted polymer (MIP)-based sensors constitute an emerging field. All the presented electrochemical sensors were successfully tested for the detection of EDCs in different types of real samples.

Label-free and highly selective electrochemical aptasensor for detection of PCBs based on nickel hexacyanoferrate nanoparticles/reduced graphene oxides hybrids

In consideration of the urgent need to determine polychlorinated biphenyls (PCBs) in the environment, a label-free and highly selective electrochemical aptasensor was constructed for determining PCBs based on nickel hexacyanoferrate nanoparticles (NiHCF NPs)/reduced graphene oxides (rGO) hybrids. NiHCF NPs/rGO hybrids with small size of about 5 nm NiHCF NPs were synthesized for the first time by in situ co-deposition of NiHCF NPs on rGO surface. In the hybrids, rGO with large area and good conductivity can supply more space for loading NiHCF NPs and improve the conductivity of the hybrids. NiHCF NPs that can be used to be act as a signal probe exhibit a couple of well-defined peaks with highly reversible redox ability and good stability. Here, PCB77 as a model molecule, the anti-PCB77 aptamer was anchored on the NiHCF NPs/rGO hybrids by covalent bonding reaction. The design aptasensor for detecting PCB77 exhibits a favorable linear response from 1.0 to 100.0 ng/L with a low detection limit of 0.22 ng/L. Meanwhile, it displays good selectivity for PCB77 detection due to the specificity and high affinity of aptamer to PCB77. Additionally, the application of the aptasensor was evaluated in real environmental samples.

Recent progress in the development of recognition bioelements for polychlorinated biphenyls detection: Antibodies and aptamers

Polychlorinated biphenyls (PCBs) are persistent pollutants, which have expanded in foods and the environment. Detection of PCBs is considered essential due to recognized side-effects of PCBs on health and the public concerns in this regard. On the other hand, due to the trace levels of these organic chlorine compounds, reliable and sensitive assays must be developed. Recognition elements are essential parts of analytical detection assays and sensors of PCBs since these elements are involved in the selective identification of the analytes of interest. Understanding the fundamentals of the recognition elements of PCBs and the benefits of the sensor strategies result in the development of next-generation recognition devices. This review aimed to highlight the recent progress in the recognition elements as key parts of biosensors. We initially, focused on the developed antibody-based biosensors for the detection of PCBs, followed by discussing the aptamers as novel recognition elements. Furthermore, the recent advancement in the development of aptamer-based solid phase extractions has been evaluated. These findings could contribute to improving the design of commercial PCB-kits in the future.

Simultaneous extraction of 32 polychlorinated biphenyls by using magnetic carbon nanocomposite based dispersive microextraction, subsequent dispersive liquid-liquid microextraction with two miscible stripping solvents, and quantitation by GC-μECD

A highly sensitive new method is described for performing dispersive microextractions. It is making use of a magnetic carbon nanocomposite and two miscible organic solvents. The method was applied to simultaneous extraction of 32 polychlorinated biphenyls (PCBs) prior to their quantitation by gas chromatography with electron capture detection. The effects of pH value of sample for both micro solid phase extraction and dispersive liquid-liquid microextraction, of the amount of sorbent, extraction time, type and volume of the miscible organic solvents and of salt addition were optimized. Figures of merit obtained under optimized conditions (sample solution: 500 ml, volume of disperser solvent, ACN, 1.5 mL; volume of extraction solvent, TCB, 30 μL; extraction time: 50 min, 20 mg magnetic sorbent, centrifuge, 5 min, 4000 rpm), include (a) preconcentration factors between 10,880 and 34,000; (b) repeatabilities of ≤14.9%, (c) detection limits between 0.01 and 0.2 ng kg-1, and (d) linear dynamic ranges from 0.05 to 100 ng kg - 1. The method was applied to the simultaneous analysis of residues in (spiked) real samples of fish, milk, packing sheet, and tap waters. Some of the analytes were found to be present in fish samples. The method is simple, rapid, and more sensitive than any of the previously reported ones. Graphical abstract Schematic presentation of simultaneous extraction of 32 polychlorinated biphenyls (PCBs) by using magnetic carbon nanocomposites (MCNs) based dispersive microextraction (M-SPE), subsequent dispersive liquid-liquid microextraction (DLLME) with two miscible stripping solvents, and quantitation by GC-μECD.