Charge Density-Regulated Microchannel-Based Electrochemiluminescence Sensor for Hydrogen Sulfide Detection with a Highly Efficient Accumulation Strategy.

The electrochemiluminescence (ECL) intensity can be regulated by ionic current passing through the microchannel, which broadened the regulation of the ECL sensors. But in the early reported sensors, the electrostatic repulsion and steric hindrance caused few targets to approach the interface of the microchannel driven by concentration difference, which reduced the detection efficiency and prolonged the detection period. In this study, different accumulation strategies, such as a positive electric field and different polarity electric fields, were designed to accumulate targets in the microchannel. The interaction of azide groups and hydrogen sulfide served as a research model. Hydrogen sulfide can react with the negatively charged azide groups in the microchannel surface to produce positively charged amino groups, decreasing the negative charge density of the microchannel and thus altering the ionic current and ECL intensity. The accumulation of hydrogen sulfide at the microchannel tip can increase the collision probability with azide groups to improve the detection efficiency, and the integration of accumulation and reaction can shorten the detection period to 28 min. The hydrogen sulfide concentration on the microchannel tip accumulated by applying different polarity electric fields was 22.3-fold higher than that accumulated by applying a positive electric field. The selected research model broadened the application range of a microchannel-based ECL sensor and confirmed the universality of the microchannel-based ECL sensor.

Photoelectrochemical Sensor for H2S Based on a Lead-Free Perovskite/Metal-Organic Framework Composite.

Halide perovskites have emerged as a highly promising class of photoelectric materials. However, the application of lead-based perovskites has been hindered by their toxicity and relatively weak stability. In this work, a composite material comprising a lead-free perovskite cesium copper iodide (CsCu2I3) nanocrystal and a metal-organic framework (MOF-801) has been synthesized through an in situ growth approach. The resulting composite material, denoted as CsCu2I3/MOF-801, demonstrates outstanding stability and exceptional optoelectronic characteristics. MOF-801 may serve a dual role by acting as a protective barrier between CsCu2I3 nanocrystals and the external environment, as well as promoting the efficient transfer of photogenerated charge carriers, thereby mitigating their recombination. Consequently, CsCu2I3/MOF-801 demonstrates its utility by providing both stability and a notably high initial photocurrent. Leveraging the inherent reactivity between H2S and the composite material, which results in the formation of Cu2S and structural alteration, an exceptionally sensitive photoelectrochemical sensor for H2S detection has been designed. This sensor exhibits a linear detection range spanning from 0.005 to 100 µM with a remarkable detection limit of 1.67 nM, rendering it highly suitable for precise quantification of H2S in rat brains. This eco-friendly sensor significantly broadens the application horizon of perovskite materials and lays a robust foundation for their future commercialization.

Portable Sensor for Aflatoxin B1 Based on the Regulation of Resistance of a Microchannel Using a Multimeter as Readout.

Changes in the charge density on the inner surface of the microchannel can modulate the ion concentration at the tip, thus causing changes in the resistance of the system. In this study, this property is adopted to construct a portable sensor using a multimeter and aflatoxin B1 (AFB1) is used as the model target. Initially, the cDNA/aptamer complex is modified in the microchannel. The inner microchannel surface's charge density is then altered by the recognition of the target, leading to a change in the system's resistance, which can be conveniently monitored using a multimeter. Critical parameters influencing the performance of the system are optimized. Under optimum conditions, the resistance is linearly related to the logarithm of AFB1 concentration in the range of 100 fM-10 nM and the detection limit is 46 fM (S/N = 3). The resistive measurement is separated from the recognition reaction of the target, reducing the matrix interference during the detection process. This sensor boasts high sensitivity and specificity coupled with commendable reproducibility and stability. It is applied to assay the AFB1 content successfully in an actual sample of corn. Moreover, this approach is cost-effective, user-friendly, and highly accurate.

Dual Self-Amplification Homogeneous Electrochemiluminescence Biosensor for Terminal Deoxynucleotidyl Transferase Activity Based on Controlling the Surface Morphology and Charge of Reporter Nanoparticles.

Terminal deoxynucleotidyl transferase (TdT) is upregulated in several types of leukemia and is considered a disease biomarker and a potential therapeutic target for leukemia. In this research, a homogeneous electrochemiluminescence (ECL) method based on the control of surface charge and morphology of tris (2,2'-bipyridine) ruthenium(II) chloride hexahydrate-doped silica nanoparticles (Ru@SiO2 NPs) has been designed for TdT activity detection. A small amount of short single-stranded DNA (ssDNA) was modified onto the surface of Ru@SiO2 NPs, and the nanoparticles with a slight positive charge experienced electrostatic attraction with the indium tin oxide (ITO) electrode with a negative charge, so relatively high ECL signals had been detected. Under the action of TdT, the ssDNA was significantly elongated, carrying numerous negative charges on its phosphate backbone, so the overall negative charge of the reporter nanoparticles was enhanced, resulting in a strong electrostatic repulsion with the ITO electrode. Simultaneously, the long ssDNA wrapped around the nanoparticles hindered the approach of the coreactant. Due to the dual effects, the ECL response of the system decreased. The constructed biosensor exhibited excellent sensitivity toward TdT over a range spanning from 1 to 100 U/L. The limit of detection is as low as 1.78 U/L. The developed approach was effectively applied to detect TdT activity in leukemic patients' leukocyte extracts.

Dual-Signal Mode Ratiometric Photoelectrochemical Sensor Based on G-Quadruplex Hole Transport for Rapid and Sensitive Detection of miRNA-210.

For rapid and sensitive detection of miRNA-210, which is important for improving the reliability of clinical diagnosis of breast cancer, a dual-signal mode ratiometric photoelectrochemical (PEC) sensor based on a Au/GaN photoanode is proposed. First, a DNA probe was designed that could complement the target miRNA-210. Then, another G-rich DNA sequence was designed to mismatch the probe and form a double-stranded DNA (dsDNA). Upon addition of the target, the dsDNA unwinds from its binding site and releases G-rich single-stranded DNA. In the presence of Mg2+ and K+, this single-stranded DNA molecule spontaneously forms a G-quadruplex structure, facilitating the rapid transport of photogenerated holes, thereby increasing the photocurrent response of Au/GaN and enabling sensitive label-free detection of miRNA-210. By control of different pH values, a response signal was generated at pH 8, while a reference signal was produced at pH 5. The designed PEC system shows a high potential for the development of miRNA-210 detection. Ultimately, the response signal-to-reference signal ratio was used as the variable, and a broad linear span ranging from 10 fM to 1 nM (R2 = 0.993) has been exhibited, with a detection threshold of 3 fM (S/N = 3). The designed PEC platform shows potential for the development of other disease markers.

Low-Background Signal-On Homogeneous Electrochemiluminescence Biosensor for Hepatitis B Virus Detection Based on the Regulation of the Length of DNA Modified on the Nanoparticles by CRISPR/Cas12a and Hybridization Chain Reaction.

In this work, combined with the high amplification efficiency of hybridization chain reaction (HCR), high specificity of the CRISPR/Cas12a system, and convenience of the homogeneous electrochemiluminescence (ECL) assay based on the regulation of negative charge on the reporting probes, a sensitive ECL biosensor for hepatitis B virus DNA (chosen as a model target) had been developed. The initiator chain trigger DNA that can induce HCR amplification is modified on the surface of ruthenium bipyridine-doped silica nanoparticles (Ru@SiO2 NPs) first, and large amounts of negative charges modified on the particles were achieved through the HCR amplification reaction. The efficiency of the nanoparticles reaching the negatively charged working electrode can be regulated and realize the change of the ECL signal. In addition, long DNA on the surface of the luminescent body may prevent the coreactant from entering the pore to react with ruthenium bipyridine. These factors combine to produce a low-background system. The presence of the target can activate the CRISPR/Cas12a system and make trigger DNA disappear from the nanoparticle surface, and strong ECL can be detected. The sensor does not require a complex electrode modification; therefore, it has better reproducibility. Additionally, due to dual signal amplification, the sensor has a high sensitivity. In the range of 10 fM to 10 nM, the ECL intensity exhibits a strong linear relationship with the logarithm of the target concentration, and the detection limit is 7.41 fM. This sensor has shown high accuracy in detecting clinical samples, which holds significant potential for application in clinical testing.

A photoelectrochemical aptasensor for tetracycline based on the self-assembly of 2D MoS2 on a 3D ZnO/Au/ITO electrode.

Two-dimensional (2D) layered MoS2 has good dispersion and adsorption properties, but being a narrow bandgap semiconductor limits its application in photoelectric sensing. In this study, a homogeneous photoelectrochemical sensor based on three-dimensional (3D) ZnO/Au/2D MoS2 is proposed for the ultrasensitive detection of tetracycline (TET). MoS2 is uniformly embedded on the 3D ZnO/Au surface by ordered self-assembly. The physical method of π-π interaction of MoS2 replaces the conventional use of chemically modifying aptamers on the electrode material surface. Under optimal conditions, this method has been successfully applied to the detection of TET in milk, honey, pig kidney and pork samples with reliable results. We believe that this study presents a method for the preparation of sensing carriers and target detection with great potential for application.

Oxygen-induced dual-signal point-of-care testing aptasensor for aflatoxin B1 detection using platinum nanoparticle catalysis in visual fluorometry and gravimetry.

Point-of-care testing (POCT) has experienced rapid development owing to its advantages of rapid testing, low cost and strong operability, making it indispensable for analyte detection in outdoor or rural areas. In this study, we propose a novel method for the detection of aflatoxin B1 (AFB1) using a dual-signal readout approach within a unified system. This method employs dual channel modes, namely visual fluorescence and weight measurements, as the signal readouts. Specifically, a pressure-sensitive material is utilized as a visual fluorescent agent, its signal can be quenched in the presence of high oxygen pressure. Additionally, an electronic balance, commonly used for weight measurement, is adopted as another signal device, where the signal is generated through the catalytic decomposition of H2O2 by platinum nanoparticles. The experimental results demonstrate that the proposed device enables accurate AFB1 detection within the concentration range of 1.5-32 µg mL-1, with a detection limit of 0.47 µg mL-1. Moreover, this method has been successfully applied for practical AFB1 detection with satisfactory results. Notably, this study pioneers the use of a pressure-sensitive material as a visual signal in POCT. By addressing the limitations of single-signal readout approaches, our method fulfills requirements of intuitiveness, sensitivity, quantitative analysis and reusability.

Ultrasensitive photoelectrochemical detection of glutathione based on the multifunctional catalytic properties of phosphotungstic acid.

A novel photoelectrochemical (PEC) sensor was constructed for the highly sensitive detection of reduced glutathione (GSH) based on the multiple catalytic properties of phosphotungstic acid (PTA). In this work, the catalytic properties of PTA were applied to PEC sensing for the first time and interpreted in detail. First, PTA as an electron acceptor can inhibit the complexation of photogenerated electron-hole pairs in p-Cu2O, thus significantly increasing the photogenerated current of p-type semiconductor material Cu2O. Secondly, when GSH is oxidized to oxidized glutathione (GSSG) by photogenerated holes on the photocathode, PTA is able to reduce GSSG to GSH by transferring protons, forming a redox cycle regeneration process of GSH. Finally, the relatively large amount of PTA in the background solution was able to pre-oxidize interfering substances such as L-cysteine and ascorbic acid, which improved the selectivity of the method. Under the optimal experimental conditions, the linear range of the PEC sensor response to GSH was 0.050-100 nmol L-1, with a detection limit as low as 0.017 nmol L-1 (S/N = 3), which can be applied to the detection of GSH content in cell lysate samples.

Multicolor Biosensor for Trypsin Detection Based on the Regulation of the Peroxidase Activity of Bovine Serum Albumin-Coated Gold Nanoclusters and Etching of Gold Nanobipyramids.

The detection of trypsin is significantly important for both clinical diagnosis and disease treatment. In this study, an innovative multicolor sensor for trypsin detection has been established based on the regulation of the peroxidase activity of bovine serum albumin-coated gold nanoclusters (BSA-Au NCs) and efficient etching of gold nanobipyramids (Au NBPs). BSA-Au NCs have slight peroxidase enzyme activity and can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate TMB+, while trypsin can hydrolyze BSA ligands on the surface of BSA-Au NCs, thus exposing more catalytic active sites of BSA-Au NCs and resulting in the enhancement of the peroxidase activity of BSA-Au NCs, hence more TMB+ is generated. Under acidic conditions, TMB+ can etch Au NBPs efficiently, consequently affecting the aspect ratio of Au NBPs accompanied by the ultraviolet-visible (UV-vis) spectra blue shifting of the system. Furthermore, this also results in color variations that can be distinguished and recognized by naked eyes without any expensive and sophisticated instruments. This multicolor sensor has an available linear relationship with the logarithm of the trypsin concentration in the range of 0.1-100 µg/mL, and the detection limit is 0.045 µg/mL. The designed sensor has been used to detect the concentration of trypsin in human serum samples from healthy individuals and pancreatitis patients with satisfactory results.

Electrochemiluminescence biosensor for DNA adenine methylation methyltransferase based on CRISPR/Cas12a trans-cleavage-induced dual signal enhancement.

In this work, an electrochemiluminescence (ECL) biosensor with dual signal enhancement was constructed and used for DNA adenine methylation methyltransferase (Dam MTase) detection. At present of Dam MTase, restriction endonuclease (DPnI) cleaves hairpin DNA (HP) and releases the HP stem end as a single strand that can activate CRISPR/Cas12a trans-cleavage activity. Assisted by trans-cleavage, the distance between the signal quenching factor ferrocene (Fc) and the ECL signal unit increased, and the repulsion between the signal unit and the Indium Tin Oxides (ITO) electrode decreased. The above results resulted in an enhanced ECL signal. ECL intensity has a good linear relationship with the logarithm of Dam MTase concentration in the range of 5-70 U/mL with a detection limit of 23.4 mU/mL. The proposed biosensor was successfully utilized to detect of Dam MTase in serum samples.

Enhanced Sensing Performance of a Microchannel-Based Electrochemiluminescence Biosensor for Adenosine Triphosphate via a dsDNA Superstructure Amplification Strategy.

The sensing performance of a microchannel-based electrochemiluminescence (ECL) biosensor is related to the change ratio of charge density on the surface of microchannels caused by a target recognition reaction. In this study, adenosine triphosphate (ATP) served as a model target. The dsDNA superstructures containing a capture probe (CP, containing an ATP aptamer sequence) and alternating units of ssDNA probes of P1 and P2, CP/(P1/P2)n, were grafted onto the inner wall of microchannels first. The CP in dsDNA superstructures captured ATP molecules, causing the release of dsDNA fragments containing alternating units of P1 and P2, (P1/P2)n. The target recognition reaction significantly changed the charge density of microchannels, which altered the ECL intensity of the (1,10-phenanthroline)ruthenium(II)/tripropylamine system in the reporting interface. The ECL intensity of the constructed system had a linear relationship with the logarithm of ATP concentration ranging from 1 fM to 100 pM with a detection limit of 0.32 fM (S/N = 3). The biosensor was successfully applied to detect ATP in rat brains.

Electrochemiluminescence biosensor for HPV16 detection based on the adjusting of steric hindrance effect coupled with Exonuclease III amplification strategy.

The effect of steric hindrance of electrode surface can affect the diffusion of the Ru(bpy)32+ toward electrode and thus in turn affect the ECL performance of the system. In this study, this character had been adopted to develop a biosensor for HPV DNA detection. Exonuclease III (Exo III) signal amplification strategy had been applied to realize signal amplification. First, hairpin probes (HP) was anchored on the surface of electrode as capture probes, HP can resistant to the hydrolyzation of Exo III due to its 3'-protruding termini. Without the target, a large amount of cDNA modified Au nanocages (AuNCs-cDNA) can hybridize with HP and connected to surface of electrode, weak ECL signals can be detected since Ru(bpy)32+ can not diffuse freely to the electrode surface because of the steric hindrance of AuNCs-cDNA. In the presence of the target, HP can hybridize with the target to form double-stranded DNA (dsDNA) with a blunt 3' terminus, due to the high preference of Exo III for cleaving dsDNA with a blunt 3' termini, HP in dsDNA was hydrolyzed, and the target which formed dsDNA was released to hybridize with another HP, inducing the Exo III assisted amplification strategy. Due to the reduction of HP on electrode surface, the amount of AuNCs-cDNA connected to the electrode surface become small, a high ECL signal can be detected. Under the optimal conditions, the ECL response of the system has a linear relationship with logarithm of target DNA concentration in the range of 10 fM to 100 pM, and a detection limit of 3.54 fM (S/N = 3). The proposed biosensor has high sensitivity and selectivity, which had been applied to the detection of target DNA in real sample and the satisfied results had been obtained. This system also can detect different targets by changing the DNA sequence easily.

Electrochemiluminescence aptasensor for vascular endothelial growth factor 165 detection based on Ru(bpy)32+/Au nanoparticles film modified electrode and double signal amplification.

Vascular endothelial growth factor (VEGF165) is a signal protein that plays a central role in the regulation of angiogenesis and can stimulate angiogenesis. The development of highly sensitive and selective detection method for VEGF165 is very important for disease diagnosis and follow-up treatment monitoring. In this study, an electrochemiluminescence (ECL) aptasensor for VEGF165 has been developed based on quench of H2O2 toward Ru(bpy)32+/TPrA ECL system and RecJf exonuclease induced target recovery and hybridization chain reaction (HCR) as amplification strategy. The presence of VEGF165 makes a large number of glucose oxidase (GOD) fixed on the electrode surface through the double signal amplification strategies. The present of GOD cause the production of a large amount of H2O2 near the electrode surface under excess amount of glucose, resulting in the inhibition of the ECL signal of Ru(bpy)32+/Au nanoparticles (Ru(bpy)32+/AuNPs) film fixed on the electrode surface. The ECL response of the designed biosensor has a good linear relationship with the logarithm of the concentration of VEGF165 in the range of 0.5 pg/mL to 500 ng/mL with a detection limit of 0.2 fg/mL. The VEGF165 in serum samples has been detected by the proposed aptasensor with satisfactory results.

A multicolor biosensor for alkaline phosphatase activity detection based on the peroxidase activity of copper nanoclusters and etching of gold nanorods.

Alkaline phosphatase (ALP) plays a vital role in clinical diagnoses and biomedical research. It is important to develop some convenient but sensitive methods for ALP activity detection. In this study, a multicolor biosensor for ALP activity has been developed based on the peroxidase activity of copper nanoclusters (CuNCs) and etching of gold nanorods (AuNRs). The presence of CuNCs can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce blue TMB+. In acid solution, TMB+ can cause the etching of AuNRs accompanied by a significant color change of the system. The presence of sodium pyrophosphate (PPi) can inhibit the peroxidase activity of CuNCs, which can be recovered after the addition of ALP. Different ALP added results in the recovery of the catalytic activity of CuNCs to different degrees and generates different amounts of TMB+. This consequently affected the morphology of the AuNRs in the system and results in the output of a vivid color change, which can be recognized with the naked eyes easily without any complicated instruments. The biosensor has a linear relationship with ALP activity in the range of 10.0-80.0 U L-1, and the detection limit is 4.6 U L-1. The proposed method has been applied to detect ALP activity in human serum samples with satisfactory results.

Sensitive Electrochemiluminescence Biosensor Based on the Target Trigger Difference of the Electrostatic Interaction between an ECL Reporter and the Electrode Surface.

The discrepancy of the electrostatic interaction of negatively charged signal molecules to long and short DNA strands of the modified electrode surface has been used for the first time to the develop an electrochemiluminescence (ECL) biosensor for human papillomavirus 16 (HPV 16) DNA detection. The short single-stranded capture probe (CP) was modified first on the surface of the gold electrode, which only has a small amount of negative charge. The electrostatic interaction between the negatively charged tris(2,2'-bipyridyl) ruthenium(II) chloride hexahydrate-doped SiO2 nanoparticles (Ru@SiO2 NPs) and CP is weak, hence Ru@SiO2 NPs easily diffuse to the surface of the electrode to generate a strong ECL signal. Hybrid chain reaction (HCR) amplification products (long strand dsDNA) were prepared in homogeneous solution in advance. When the target was present, the dsDNA can be connected on the electrode surface and cause the enhancement of the negative charge on the electrode surface. Owing to electrostatic interaction and steric hindrance, Ru@SiO2 NPs are difficult to diffuse to the electrode surface, resulting in a significantly reduced ECL signal. The decrease of ECL signal is linearly correlated with the logarithm of the HPV concentration under optimal conditions, with the detection range being 0.1 fM -5 pM with a limit of 1.41 aM. This innovative methodology expands the application of electrostatic interaction in ECL sensing, but can also easily develop biosensors for detecting other targets by changing the DNA sequence used in this strategy.

Multicolor hydrogen sulfide sensor for meat freshness assessment based on Cu2+-modified boron nitride nanosheets-supported subnanometer gold nanoparticles.

Hydrogen sulfide (H2S) has emerged as an important indicator in the spoilage process of meat. In this study, a mimetic enzyme based on Cu2+-modified boron nitride nanosheets-supported gold nanoparticles (AuNPs/Cu2+-BNNS) was synthesized, which can be used to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). The H2S gas can inhibit the activity of AuNPs/Cu2+-BNNS toward catalytic oxidation of TMB. Meanwhile, the usage of headspace method could avoid most interferences in the rotten sample. Various concentrations of TMB+ could change the aspect ratio of the gold nanoroads (AuNRs), which results in vivid color changing and UV-vis spectra shifting. The sensor had a good linear relationship with H2S concentration ranging from 10.0 to 90.0 µmol/L, and the detection limit is 7.8 µmol/L. The AuNPs/Cu2+-BNNS sensors were successfully applied to detect H2S produced by meat spoilage with satisfying results.

Electrochemiluminescence Aptasensor for Charged Targets through the Direct Regulation of Charge Density in Microchannels.

The change of surface charge density can cause many changes in physical or chemical properties and has been applied to design many sensitive sensors. Ochratoxin A (OTA) is a negatively charged target in neutral or alkaline solutions. In this work, a microchannel-based electrochemiluminescence (ECL) aptasensor for OTA detection based on this character had been designed. The charged target directly combined with functionalization layers of the microchannels, which caused surface charge density variation and therefore resulted in the change of ECL intensity of the (1,10-phenanthroline)ruthenium(II)/tripropylamine system. The decrease of ECL intensity is linearly dependent on OTA concentration ranging from 0.5 to 4 ng mL-1 with a detection limit down to 0.17 ng mL-1. This strategy has the advantages of simple interface chemistry design and universality, which offers a guiding significance for the charged target assay.

Single nanoparticle identification coupled with auto-identify algorithm for rapid and accurate detection of L-histidine.

In this work, an auto-identify sensor was constructed for rapid and high-precision detection of L-histidine. The proposed strategy is based on the auto-identify algorithm and the aggregation of alkynyl and azide functionalized gold nanoparticles induced by the Cu+ catalyzed azides and alkynes cycloaddition (CuAAC) reaction. Specially, the color of scattering light spots for the aggregated gold nanoparticle (AuNPs) caused by CuAAC reaction was quite different from that of the monomers. However, L-histidine can bind to Cu2+ and inhibits the production of Cu+, hence preventing the aggregation of AuNPs. Therefore, there is a distinct change of color as the addition of L-histidine under dark-field microscopy. Then, L-histidine can be quantitatively detected by combining the color change with the Meanshift algorithm accurately and automatically. Such proposed method has been successfully applied for the detection of L-histidine in serum sample with satisfying result.

Electrochemiluminescence biosensor for thrombin detection based on metal organic framework with electrochemiluminescence indicator embedded in the framework.

Ru(dcbpy)32+-polyethyleneimine-L-lysine (Ru-PEI-L-lys) had been immobilized on metal organic frameworks (ZIF-8) to form an electrochemiluminescent(ECL) indicator (Ru-PEI-L-lys-ZIF-8). In this ECL indicator, PEI-L-lys is used as a co-reactant. Platinum nanoparticles (PtNPs) has been mixed with Ru-PEI-L-lys-ZIF-8 to form a thin film to increase the electron transfer rate and enhanced the ECL response of the system. The prepared material had been characterized carefully and been combined with high selectivity of aptamer to develop a ECL biosensor for thrombin detection. RecJf exonuclease (an ssDNA specific exonuclease) assistant target recycling amplification has been adopted to enhance the sensitivity of the system. The ECL response of the system has a linear relationship with logarithm of thrombin concentration in the range of 1 fM to 10 pM with a detection limit of 0.02 aM. This work not only provides a new strategy for the design and synthesis of high performance and stable ECL indicator, but also opens up a new approach for the development of highly sensitive ECL sensors for biological analysis.