Colorimetric and electrochemical integrated dual-mode detection of glucose by utilizing CoOOH@Cu nanosheets as peroxidase mimetics

Ion-imprinting strategy towards a novel two-in-one copper-based nanozyme for sensitive electrochemical-colorimetric dual-mode detection of paracetamol

Dual-mode sensors integrating multifunctional nanozymes are highly sought by the analytical chemistry community. However, rational design of nanozymes containing both metal single atoms (SAs) and atomic clusters (ACs) for dual-mode sensing remains a challenge. Herein, we designed and synthesized a novel Cu-based nanozyme system based on Cu SAs/ACs anchored on a N-doped chitosan-derived carbon support (CuSAs/ACs@NC) using a tandem ion imprinting-pyrolysis-etching strategy. Compared with Cu SAs or Cu nanoparticles on the chitosan-derived carbon support, the proposed CuSAs/ACs@NC nanozyme exhibits superior electrocatalytic activity and peroxidase-mimicking activity. Benefitting from the synergistic effect of Cu SAs and ACs which enhances electron transport, the CuSAs/ACs@NC nanozyme allows electrochemical-colorimetric dual-mode detection of paracetamol (PA) based on the amplification of the electrochemical signal of PA and the inhibition effect of PA on peroxidase activity, respectively. The linear range of the electrochemical mode is 2.00-473.00 μM with a detection limit of 0.48 μM, while that of the colorimetric mode is 0.25-100.00 μM with a detection limit of 0.10 μM. Moreover, this dual-mode sensor exhibits favorable reproducibility (relative standard deviation ≤ 4.00 %), stability (maintaining stable after 4 months of storage), and accuracy (recoveries of 91.5-114.9 %). Satisfyingly, the developed dual-mode method allows accurate PA detection in commercial drugs with relative deviation below 1.5 %. This work presents a new strategy for the preparation of SAs/ACs as multifunctional nanozymes for sensing, drug monitoring, and clinical diagnosis.

Colorimetric aptasensors for sensitive low-density lipoprotein detection based on reduced oxide graphene@molybdenum disulfide-ferrocene nanosheets with peroxidase-like activity

Low-density lipoprotein (LDL) is a key biomarker for cardiovascular disease (CVD) risk assessment. Monitoring LDL for the early diagnosis of CVD and its complications is an important clinical analysis tool. In this work, a novel colorimetric aptasensor for LDL detection was constructed via reduced graphene oxide@molybdenum disulfide-ferrocene-carboxylic nanosheets (rGO@MoS2-Fc) with excellent peroxidase-like activity. On this basis, the LDL aptamer (LDLapt) immobilized on the surface of rGO@MoS2-Fc served as a signal probe (rGO@MoS2-Fc/LDLapt), while the unmodified LDLapt served as a capture probe. When LDL was present, it was recognized by the LDLapt and rGO@MoS2-Fc/LDLapt to form an rGO@MoS2-Fc/LDLapt/LDL/LDLapt sandwich-type conjugate with excellent enzymatic catalytic properties that can catalyze the generation of hydroxyl radicals (·OH) from hydrogen peroxide (H2O2), which in turn oxidized the colorless substrate o-phenylenediamine (OPD) to the yellow compound 2,3-diamino phenothiazine (DAP). In addition, the catalytic mechanism of the reaction was confirmed to be induced by ·OH through free radical experiments. The aptasensor had a linear range of 15.0 to 200.0 μg mL-1, and a limit of detection (LOD) of 2.199 μg mL-1. Overall, the assay has high selectivity, sensitivity and operability, showing broad application prospects in the clinical diagnosis of CVD.

Multimodal biosensing systems based on metal nanoparticles

Biosensors are currently among the most commonly used devices for analysing biomarkers and play an important role in environmental detection, food safety, and disease diagnosis. Researchers have developed multimodal biosensors instead of single-modal biosensors to meet increasing sensitivity, accuracy, and stability requirements. Metal nanoparticles (MNPs) are beneficial for preparing core probes for multimodal biosensors because of their excellent physical and chemical properties, such as easy regulation and modification, and because they can integrate diverse sensing strategies. This review mainly summarizes the excellent physicochemical properties of MNPs applied as biosensing probes and the principles of commonly used MNP-based multimodal sensing strategies. Recent applications and possible improvements of multimodal biosensors based on MNPs are also described, among which on-site inspection and sensitive detection are particularly important. The current challenges and prospects for multimodal biosensors based on MNPs may provide readers with a new perspective on this field.

Construction of smartphone-adapted signal visualization platform for dual-mode detection of H2S based on integrated metal-organic framework nanoprobes

Hydrogen sulfide (H2S) is a toxic contaminant and has great influence on many physiological processes. Due to various pathophysiological roles and environmental pollution problems, it is necessary to construct and develop simple and portable monitoring sensors for the precise detection of H2S. Herein, we developed a smartphone-adapted dual-mode detection platform by integrating the colorimetric and photothermal imaging analysis into a metal-organic framework-based chip (ZIF-8/Cu). Due to the nanoconfinement effect of ZIF-8, small-sized plasmonic CuS could be in-situ formed during the detection procedure of H2S and endowed the chips with excellent photothermal properties. By constructing a smartphone-adapted photothermal imager, the metal-organic framework-based chip could achieve a portable photothermal imaging analysis of H2S. Moreover, as the formed CuS was a good peroxidase-like nanozyme, the chips could also be used to trigger the enzymic catalytic reaction toward the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2, thus providing another colorimetric sensing mode by using a smartphone App. In this smartphone-adapted visualization platform, the portable chemosensors could simultaneously achieve double detection modes at one electrode, which provided a new pathway for the accurate detection of H2S and circumvented the false-positive or negative errors during the detection process. Besides, by using the finite difference time domain (FDTD) simulation method, the in-depth mechanism, including the plasmonic effect and spatial electromagnetic field distribution, was explored to provide a possible reason for the excellent sensing performance of the dual-mode visualization platform. This work provides a new insight into the construction of the accurate, portable and smart sensing platform in the visual screening of H2S.

Two-step resonance-energy-transfer-based ratiometric biosensor for sensing and annihilation of Staphylococcus aureus

A two-step resonance energy transfer (RET)-based fluorescence/electrochemiluminescence (FL/ECL) biosensor was developed for ratiometric measurement and annihilation of Staphylococcus aureus (S. aureus). Using coupled dual-recognition-triggered target conversion with the catalytic hairpin assembly (CHA) technique, the monitoring of S. aureus was obtained at the single-cell level.

A colorimetric/electrochemical sensor based on coral-like CuCo2O4@AuNPs composites for sensitive dopamine detection

As a central neurotransmitter, DA (dopamine) plays a vital part in human metabolism, and its accurate detection is of great significance in disease diagnosis. In this work, we used Cu/Co bimetallic metal-organic frameworks (MOFs) as templates and gold nanoparticles (AuNPs) to construct novel nanocomposite coral-like CuCo2O4@AuNPs with strong peroxidase activity and electrochemical response. The coral-like CuCo2O4@AuNPs showed excellent peroxidase activity, and the Km value was as low as 0.358 mM. In the presence of H2O2, the colorless substrate 3,3',5,5', -tetramethylbenzidine (TMB) can be catalytically oxidized into a blue product. Simultaneously, coral-like CuCo2O4@AuNPs, as an electroactive substance, possess strong electrocatalytic activity, which enhances the electron-transfer rate and promotes excellent current response. In the presence of DA, coral-like CuCo2O4@AuNPs can catalyze the oxidation of DA to dopaquinone, which further enhances the electrochemical signal. In addition, DA captures hydroxyl radicals and inhibits the oxidation of TMB, resulting in an obvious color change (blue turns colorless) and realizing colorimetric detection with the naked eye. On this basis, we successfully established a dual-mode colorimetric/electrochemical sensor using coral-like CuCo2O4@AuNP nanocomposites as a dual-signal probe. Combining colorimetric and electrochemical detection, the sensor achieved a wide linear range (0-1 mM) and a low detection limit (0.07 μM) for DA concentration. It was also successfully used for the detection of DA in human serum and urine with good results. In summary, this work provides an intuitive, economical, sensitive, and promising platform for DA detection.

Label-free dual-mode sensing platform based on target-regulated CRISPR-Cas12a activity for ochratoxin A in Morinda officinalis

Many traditional Chinese herbs are susceptible to ochratoxin A (OTA), a potent mycotoxin, which causes serious effects on the quality of the herb and on people's health. The development of methods to detect OTA is extremely important. Most methods for detecting OTA are based on a single-signal output mode, which might be easily influenced by complex environmental conditions. In this research, by taking advantage of the cleavage of DNA by target-induced CRISPR-Cas12a activity and the difference in electrostatic force of DNA to different charge electrochemiluminescent (ECL) and electrochemical (EC) probes, a biosensor is developed for the detection of OTA. First, the CRISPR-Cas12a system consists of a well-designed crRNA, its complementary strand (also as an aptamer for OTA), and Cas12a. Without the target, this CRISPR-Cas12a system is in the "activated stage", which digests hairpin DNA on the electrode, resulting in a weak ECL signal and strong current response. With the introduction of OTA bound with the aptamer, CRISPR-Cas12a activity is inhibited ("locked stage"). Thus, hairpin DNA remained intact on the electrode, resulting in recovery of the ECL signal and attenuation of the current intensity. As a result, this label-free dual-mode sensing platform realizes an assay for OTA in Morinda officinalis. This target-regulated CRISPR-Cas12a activity-sensing platform with dual-mode output not only provides high sensitivity (due to the CRISPR-Cas12a system), but also has good anti-interference ability against complex substrates (due to dual-mode output), and exhibits a broad range of prospects for application.