Rolling circle amplification promoted magneto-controlled photoelectrochemical biosensor for organophosphorus pesticides based on dissolution of core-shell MnO2 nanoflower@CdS mediated by butyrylcholinesterase

Handgrip-Ring Structure Sensing Probe Assisted Multiple Signal Amplification Strategy for Sensitive and Label-Free Single-Stranded Nucleic Acid Analysis

Precise and efficient identification of single-stranded nucleic acids is crucial for both pathological research and early diagnosis of diseases, such as cancers. Therefore, we have devised a novel biosensor that utilizes an elegantly designed handgrip-ring structure sensing probe to enhance the detection sensitivity and reduce background signals. The handgrip-ring structure sensing probe combines ring padlock-based target recognition and hairpin structure probe-based signal amplification. The target sequences form a binding interaction with the ring padlock in the sensing probe, leading to the elongation of the single-stranded chain with the assistance of polymerase. This elongation step results in the release of the hairpin probe, triggering a signal amplification process. This design significantly minimized the potential discrepancies that may occur during the signal amplification process, hence bestowing the approach with a low level of background signals. By utilizing this innovative design, the current biosensor demonstrates a remarkable ability to detect miRNA with a limit as low as 376 aM and single-stranded DNA sequences with a limit as low as 45.3 aM. In addition, it possesses exceptional discrimination capabilities. The efficacy of this approach in diagnosing targets was also effectively proved by the rational redesign of the ring padlock.

Triple modal aptasensor arrays driven by CHA-mediated DNAzyme for signal-amplified atrazine pesticide accumulation monitoring in agricultural crops

Developing sensors with high selectivity and sensitivity is of great significance for pesticide analysis in environmental assessment. Herein, a versatile three-way sensor array was designed for the detection of the pesticide atrazine, based on the integration of catalytic hairpin assembly (CHA) amplification and three-mode signal transducers. With atrazine, CHA was triggered to generate abundant G-quadruplex. The produced G-quadruplex hybrid could assemble with thioflavin T (TFT) or hemin to mimic enzyme and induce the fluorescence enhancement by TFT, or the colorimetric increase by the oxidized chromogenic substrate and the naked-eye color change by inhibiting the L-cysteine-mediated aggregation of gold nanoparticles. A distinctive three-mode array was successfully constructed with convenience, on-site accessibility and high sensitivity for enzyme-free practical analysis of atrazine. It is also effective and reliable for analyzing real samples including paddy water, paddy soil and polished rice. The detection limits for atrazine were as low as 7.4 pg/mL by colorimetric observation and 0.25 pg/mL by fluorescent detection. Furthermore, the array was exploited to monitor the residue, distribution and bioaccumulation of atrazine in maize and rice for food security and environmental assessment. Hence, this work presented a versatile example for sensitive and on-site all-in-one pesticide analysis arrays with multiple signal report modes.

Recent trends in core/shell nanoparticles: their enzyme-based electrochemical biosensor applications

Improving novel and efficient biosensors for determining organic/inorganic compounds is a challenge in analytical chemistry for clinical diagnosis and research in biomedical sciences. Electrochemical enzyme-based biosensors are one of the commercially successful groups of biosensors that make them highly appealing because of their low cost, high selectivity, and sensitivity. Core/shell nanoparticles have emerged as versatile platforms for developing enzyme-based electrochemical biosensors due to their unique physicochemical properties and tunable surface characteristics. This study provides a comprehensive review of recent trends and advancements in the utilization of core/shell nanoparticles for the development of enzyme-based electrochemical biosensors. Moreover, a statistical evaluation of the studies carried out in this field between 2007 and 2023 is made according to the preferred electrochemical techniques. The recent applications of core/shell nanoparticles in enzyme-based electrochemical biosensors were summarized to quantify environmental pollutants, food contaminants, and clinical biomarkers. Additionally, the review highlights recent innovations and strategies to improve the performance of enzyme-based electrochemical biosensors using core/shell nanoparticles. These include the integration of nanomaterials with specific functions such as hydrophilic character, chemical and thermal stability, conductivity, biocompatibility, and catalytic activity, as well as the development of new hybrid nanostructures and multifunctional nanocomposites.

Recent Progress in Photoelectrochemical Sensing of Pesticides in Food and Environmental Samples: Photoactive Materials and Signaling Mechanisms

Pesticides have become an integral part of modern agricultural practices, but their widespread use poses a significant threat to human health. As such, there is a pressing need to develop effective methods for detecting pesticides in food and environmental samples. Traditional chromatography methods and common rapid detection methods cannot satisfy accuracy, portability, long storage time, and solution stability at the same time. In recent years, photoelectrochemical (PEC) sensing technology has gained attention as a promising approach for detecting various pesticides due to its salient advantages, including high sensitivity, low cost, simple operation, fast response, and easy miniaturization, thus becoming a competitive candidate for real-time and on-site monitoring of pesticide levels. This review provides an overview of the recent advancements in PEC methods for pesticide detection and their applications in ensuring food and environmental safety, with a focus on the categories of photoactive materials, from single semiconductor to semiconductor-semiconductor heterojunction, and signaling mechanisms of PEC sensing platforms, including oxidation of pesticides, steric hindrance, generation/decrease in sacrificial agents, and introduction/release of photoactive materials. Additionally, this review will offer insights into future prospects and confrontations, thereby contributing novel perspectives to this evolving domain.

Hairpin/DNA Ring Ternary Complex Initiated Rolling Circle Amplification for an Elevated Accuracy and Its Application in Analyzing Let-7a

Rolling circle amplification (RCA) is an attractive isothermal nucleic acid amplification approach and has been widely applied in constructing a variety of biosensors. However, the inevitable drawbacks of lacking enough selectivity greatly hindered further applications of RCA-based approaches. Here, we develop a novel RCA-based approach by integrating the specific target recognition capability of the hairpin/DNA ring ternary complex and multiple signal amplification and successfully applied it for let-7a detection. In this method, let-7a specifically unfolds the hairpin probe (Hp probe) in the ternary complex to induce target recycle and RCA- and DNAzyme-based signal generation. Based on this, the established approach exhibits a high selectivity to let-7a, and the response of the approach to one base pair mismatched sequences was 24.9%, indicating a significantly improved specificity. Meanwhile, the limit of detection is as low as 342 aM, which can meet the high requirement for a trace amount of miRNA detection. In all, we believe that the established approach can offer a new avenue for miRNA detection and post-tumor care.

Immobilization-free electrochemical homogeneous aptasensor for highly sensitive detection of carcinoembryonic antigen by dual amplification strategy

Electrochemical aptasensor has been widely studied, while its practical application is limited by the unavoidable variations of aptamer loading densities and low signal amplification efficiency. To overcome these restrictions, an immobilization-free and label-free electrochemical homogeneous aptasensor was constructed for carcinoembryonic antigen (CEA) assay by combining RecJ_f exonuclease-mediated target cycling strategy and rolling circle amplification technology. In this system, the pre-immobilization of aptamers or other relevant signal elements on the electrode substrate is no longer necessary, thus the electrochemical homogeneous aptasensor shows good versatility on different transducers. Moreover, the whole recognition and signal amplification process are activated instantaneously by a non-professional operation of the solution mixture. This strategy can not only increase the stability (95.1% after 30 days of storage) and reproducibility (2.12% among five independent electrodes), but also further improve the sensitivity (detection limit of fg mL^-1 level) due to the free target recognition and dual signal amplification in the homogeneous solution phase. The proposed immobilization-free electrochemical homogeneous aptasensors on different electrode substrates both achieve satisfactory results in actual sample tests, which has the potential for commercial applications and the establishment of other target platforms in the future.

Dual-ratiometric electrochemical aptasensor based on carbon nanohorns/anthraquinone-2-carboxylic acid/Au nanoparticles for simultaneous detection of malathion and omethoate

Organophosphorus pesticides (OPs) are one of the most frequently used pesticides in agriculture, and their residues in environment have caused serious human health and environmental concerns. In this work, we reported a dual-ratiometric electrochemical aptasensor based on carbon nanohorns/anthraquinone-2-carboxylic acid/Au nanoparticles (CNHs/AQ/AuNPs) for simultaneous detection of malathion (MAL) and omethoate (OMT). Here, CNHs/AQ/AuNPs composites were synthesized by a simple room temperature method, and used as a substrate to generate a reference signal (I_AQ) and enlarge response signals. Hairpin DNA was then immobilized, offering independent and specific binding sites to further adsorb MB-labelled MAL aptamer (MB-Apt1) and Fc-labelled OMT aptamer (Fc-Apt2). Upon the addition of MAL or OMT, the formation of aptamer-target complex caused the release of MB-Apt1 or Fc-Apt2 from the electrode, resulting in a decrease in I_MB or I_Fc, while I_AQ kept unchanged. Based on this principle, the ratiometric signals of I_MB/I_AQ and I_Fc/I_AQ were used to simultaneously detect MAL and OMT, offering a linear range of 3 pg mL^-1 to 3 ng mL^-1 for MAL and 10 pg mL^-1 to 10 ng mL^-1 for OMT, and no significant cross-reactivity existed. By taking advantage of the excellent conductivity and large specific area of CNHs/AQ/AuNPs and the stable two-dimensional structure of hairpin DNA, the aptasensor exhibited high sensitivity, selectivity and reliability. Our work has offered a novel way for simultaneous detection of multiple OPs.

A comprehensive review on electrochemical and optical aptasensors for organophosphorus pesticides

There has been a rise in pesticide use as a result of the growing industrialization of agriculture. Organophosphorus pesticides have been widely applied as agricultural and domestic pest control agents for nearly five decades, and they remain as health and environmental hazards in water supplies, vegetables, fruits, and processed foods causing serious foodborne illness. Thus, the rapid and reliable detection of these harmful organophosphorus toxins with excellent sensitivity and selectivity is of utmost importance. Aptasensors are biosensors based on aptamers, which exhibit exceptional recognition capability for a variety of targets. Aptasensors offer numerous advantages over conventional approaches, including increased sensitivity, selectivity, design flexibility, and cost-effectiveness. As a result, interest in developing aptasensors continues to expand. This paper discusses the historical and modern advancements of aptasensors through the use of nanotechnology to enhance the signal, resulting in high sensitivity and detection accuracy. More importantly, this review summarizes the principles and strategies underlying different organophosphorus aptasensors, including electrochemical, electrochemiluminescent, fluorescent, and colorimetric ones.

Preparation of Bi/BiOBr sensitized titania nanorod array via one-pot solvothermal method and construction of kanamycin photoelectrochemical aptasensor

In this work, a photoelectrochemical (PEC) aptasensor for detecting kanamycin (KAN) was designed based on aptamer modified Bi/BiOBr/ titania nanorod array (TiO2 NRA). Bi/BiOBr was loaded onto TiO2 NRA via...

Functional nucleic acid biosensors utilizing rolling circle amplification

Functional nucleic acids regulate rolling circle amplification to produce multiple detection outputs suitable for the development of point-of-care diagnostic devices.

Rolling Circle Amplification as a Universal Method for the Analysis of a Wide Range of Biological Targets

Detection and quantification of biotargets are important analytical tasks, which are solved using a wide range of various methods. In recent years, methods based on the isothermal amplification of nucleic acids (NAs) have been extensively developed. Among them, a special place is occupied by rolling circle amplification (RCA), which is used not only for the detection of a specific NA but also for the analysis of other biomolecules, and is also a versatile platform for the development of highly sensitive methods and convenient diagnostic devices. The present review reveals a number of methodical aspects of RCA-mediated analysis; in particular, the data on its key molecular participants are presented, the methods for increasing the efficiency and productivity of RCA are described, and different variants of reporter systems are briefly characterized. Differences in the techniques of RCA-mediated analysis of biotargets of various types are shown. Some examples of using different RCA variants for the solution of specific diagnostic problems are given.

An enhanced photoelectrochemical biosensor for colitoxin DNA based on HKUST-1/TiO2 and derived HKUST-CuO/TiO2 heterogeneous composites

HKUST-1 MOFs and its derivative HKUST-CuO were coupled with TiO₂ nanoparticles to form the heterogeneous composites of HKUST-1/TiO₂ and HKUST-CuO/TiO₂ based on their well-suitable bandgap energies (Eg). Compared with mono-component HKUST-1 or HKUST-CuO, the prepared composites displayed photoelectrochemical (PEC) response due to the synergistic effect from their heterogeneous structure. Higher photocurrent response was obtained on HKUST-CuO/TiO₂-modified ITO electrode (HKUST-CuO/TiO₂/ITO), which could be attributed to the hollow structure with a thin shell of HKUST-CuO greatly enhancing visible spectra harvesting. The CuO component in HKUST-CuO not only could accelerate electron transfer on the heterojunction interface but also effectively separate the photo-generated charge carriers (e^-1/h⁺). Based on the excellent PEC performance of prepared photoactive composite material, under visible-light excitation (λ ≥ 420 nm) and with a working potential of 0 V (vs. Ag/AgCl), the S1 (probe DNA)/HKUST-CuO/TiO₂/ITO PEC platform was successfully fabricated for colitoxin DNA detection without using ascorbic acid (AA) as an electron donor. Compared with the analysis results on S1/HKUST-1/TiO₂/ITO electrode, S1/HKUST-CuO/TiO₂/ITO displayed a wider linear response range from 1.0 × 10^-6 to 4.0 × 10^-1 nM with a lower detection limit of 3.73 × 10^-7 nM (S/N = 3), the linear regression equation was ΔI (10^-6 A) =0.5549-0.1858 log (C_S2/M), which confirmed the HKUST-CuO could improve sensitivity because of its prominent PEC property. The relative standard deviation (RSD) of the PEC sensor for target DNA detection of 2.0 × 10^-4 nM was 7.4%. The proposed DNA biosensor also possessed good specificity and stability. Hence, this reported work was a promising strategy for molecular diagnosis in the bio-analysis field. (A) Schematic illustration of the preparation process of the proposed PEC biosensors for colitoxin DNA detection. (B) The preparation process of HKUST-1 and HKUST-CuO.

Ultrasensitive zero-background photoelectrochemical biosensor for analysis of organophosphorus pesticide based on in situ formation of DNA-templated Ag2S photoactive materials

Herein, a novel signal-on photoelectrochemical (PEC) biosensor with nearly zero background noise (ZBN) was first fabricated to determine the presence of organophosphorus pesticide based on in situ formation of DNA-templated Ag₂S photoactive materials, accompanied by hybridization chain reaction (HCR) signal amplification. The capture probe (S1) on the gold nanoparticle-modified electrode can hybridize with the aptamer molecule to generate a simple PEC biosensor. In the presence of a target molecule, the aptamer molecule is released on the double-stranded DNA (dsDNA)-modified PEC biosensor. Meanwhile, the capture probe remains on the electrode and can open the DNA hairpins (H1, H2) which are rich in cytosine, to trigger the HCR reaction. The rich "C" strands are uncovered after formation of a long dsDNA polymer strand, which can assemble multiple silver ions (Ag⁺) by means of by C-Ag⁺-C chelation. Then, a large number of Ag₂S can be generated by challenging with S^2- solution, producing a satisfactory photocurrent signal. The photoactive material is formed in situ, which eliminates the laborious operation. Moreover, the signal can be highly amplified with nearly zero background noise and HCR signal amplification. Under optimal conditions, the ZBN aptasensor exhibited high sensitivity and selectivity, with a low detection limit of 2 pg mL^-1 for malathion. Importantly, the sensing platform can also be applied to determine the presence of malathion in real samples. In this assay, a novel signal-on photoelectrochemical biosensor with nearly zero background noise was first fabricated to determine the presence of organophosphorus pesticide based on in situ formation of DNA-templated Ag₂S photoactive materials, accompanied by hybridization chain reaction signal amplification.

Photoelectrochemical Aptasensors Constructed with Photosensitive PbS Quantum Dots/TiO2 Nanoparticles for Detection of Kanamycin

Kanamycin (Kana) is widely used as a veterinary medicine and its abuse causes a serious threat to human health, raising the urgent demand for detection of residual Kana in animal-derived food with high specificity and sensitivity. Here, we developed a photoelectrochemical (PEC) biosensor for rapid quantification of Kana, with lead sulfide quantum dots/titanium dioxide nanoparticles (PbS QDs/TiO₂ NPs) as a photosensitive composite, a Kana-specific DNA aptamer as a functional sensor, and ruthenium(III) hexaammine (Ru(NH₃)₆³⁺) as a signal booster. To prepare the PEC aptasensor, TiO₂ NPs, PbS QDs, and polyethyleneimine (PEI) were respectively used to modify the indium tin oxide electrode, and then the amine-terminated aptamer probe was connected to the PEI via glutaraldehyde. Finally, Ru(NH₃)₆³⁺ was attached on the surface of the aptamer to increase the photocurrent intensity. When Kana binds competitively with Ru(NH₃)₆³⁺ to the aptamer immobilized on the surface of the aptasensor, Ru(NH₃)₆³⁺ will be released from the aptamer, resulting in a decrease of the photocurrent signal. This PEC aptasensor exhibits a good linear relationship between the photocurrent shift and the logarithm of Kana concentration within the range of 1.0-300.0 nmol L^-1, and the detection limit is 0.161 nmol L^-1. Importantly, the PEC aptasensor presented good detection selectivity owing to specific interaction with Kana and was successfully implemented to quantify Kana in honey and milk, suggesting that the PEC aptasensor has the potential of rapid detection of residual Kana in animal-derived foods.

Cathodic photoelectrochemical aptasensor based on NiO/BiOI/Au NP composite sensitized with CdSe for determination of exosomes

A cathodic photoelectrochemical sensor has been developed for the determination of exosomes, based on a dual-signal reduction strategy. A heterostructure of NiO/BiOI/Au NP/CdSe was synthesized as a photoelectrochemical sensing interface, which is able to suppress the recombination of electron-hole pairs and produce a higher photocurrent. The obtained materials were characterized, and the mechanism for the generation of the cathodic photocurrent was proposed. CdSe QDs (quantum dots) modified with DNA₂ were assembled on the electrode through the hybridization with EpCAM aptamer on the surface of ITO/NiO/BiOI/Au NP. The introduction of CdSe QDs to the electrode increases the photocurrent.The recognition of exosomes with aptamer DNA led to the separation of CdSe QDs from the electrode, which in turn caused the decrease of photocurrents. Meanwhile, the big volume of exosomes hinders the electron transfer between the electrode and electrolyte. Due to the dual reduction effect, a sensitive PEC sensor was obtained with a detection limit of 1.2 × 10² particles/μL exosomes (λ_ex = 430 nm, bias voltage = - 0.1 V). The cathodic photoelectrochemical sensor showed good selectivity, performed well in a complex biological environment and could be used to distinguishbreast cancer patients from healthy individuals.

Photothermal and fluorescent dual-mode assay based on the formation of polydopamine nanoparticles for accurate determination of organophosphate pesticides

A photothermal and fluorescent dual-mode assay for sensitive organophosphate pesticides (Ops) determination is reported based on alkaline phosphatase (ALP)-inhibition-induced formation of polydopamine (PDA) nanoparticles. In the presence of ALP, ascorbic acid 2-phosphate (AAP) can be catalyzed to produce ascorbic acid (AA). AA can reduce MnO₂ nanosheets, further inhibiting the oxidation of dopamine (DA). Ops as an inhibitor for ALP activity prevents the formation of AA and the reduction of MnO₂ nanosheets. Eventually, the formation of PDA nanoparticles is promoted. The inhibitory effect of Ops on ALP activity causes obvious changes of photothermal signals and fluorescence signal at 495 nm. The detection limit (LOD) of dimethoate is 0.1 μM. The method displays excellent sensing capability for the dimethoate assay in real water with good recoveries of 99.4-107.6%. Graphical abstract A photothermal and fluorescent dual-mode biosensor for sensitive Ops detection was reported based on alkaline phosphatase (ALP)-inhibition-induced formation of polydopamine (PDA) nanoparticles. The dual-mode method significantly improved the accuracy and reliability of the results.

Photoelectrochemical aptasensor with low background noise

In photoelectrochemical (PEC) detection, enhancing the PEC signal and depressing the blank signal are conducive to improve the sensitivity. Because the carbon nanotube (CNT) effectively transfers photogenerated electrons from SnSe to the electrode, the composite nanomaterial CNTs/SnSe generates a strong PEC signal. Methionine (Met), AuNPs, and probe DNA are woven together forming a nanoprobe which is used as a quencher to quench the PEC signal of CNTs/SnSe. When the nanoprobe and CNTs/SnSe are modified onto the electrode, there is a low blank signal. In the presence of metastatic breast cancer cells, the cells interact with the aptamer of dsDNA; concomitantly, cDNA is released to trigger catalytic hairpin assembly (CHA). As a result, a new dsDNA which has an overhang is formed. The nanoprobe on the surface of the electrode hybridizes with the newly formed dsDNA. Subsequently, the nanoprobe is released from the surface of the electrode and the quenching effect between the nanoprobe and the CNTs/SnSe disappears. The PEC aptasensor is linear in the concentration range of 300-5,000 cells/mL, and the detection limit is 180 cells/mL under optimized conditions. The relative standard deviation (RSD) is 3.6% at 10,000 cells/mL. This work demonstrates a promising strategy using CNTs/SnSe as the photoactive material and Met-AuNPs as the quencher to establish a PEC aptasensor with a high PEC response and low blank signal. It can be used to detect bioactive substances at ultralow levels prospectively. Graphical abstract.