Novel Porphyrin Zr Metal–Organic Framework (PCN-224)-Based Ultrastable Electrochemiluminescence System for PEDV Sensing

CRISPR/Cas12a-Responsive Smart DNA Hydrogel for Sensitive Electrochemiluminescence Detection of the Huanglongbing Outer Membrane Protein Gene

Citrus Huanglongbing (HLB) is known as the cancer of citrus, where Candidatus Liberibacter asiaticus (CLas) is the most prevalent strain causing HLB. In this study, we report a novel electrochemiluminescence (ECL) biosensor for the highly sensitive detection of the CLas outer membrane protein (Omp) gene by coupling rolling circle amplification (RCA) with a CRISPR/Cas12a-responsive smart DNA hydrogel. In the presence of the target, a large number of amplicons are generated through RCA. The amplicons activate the trans-cleavage activity of CRISPR/Cas12a through hybridizing with crRNA, triggering the response of smart DNA hydrogel to release the encapsulated AuAg nanoclusters (AuAg NCs) on the electrode and therefore leading to a decreased ECL signal. The ECL intensity change (I0 - I) is positively correlated with the concentration of the target in the range 50 fM to 5 nM, with a limit of detection of 40 fM. The performance of the sensor has also been evaluated with 10 samples of live citrus leaves (five HLB negative and five HLB positive), and the result is in excellent agreement with the gold standard qPCR result. The sensing strategy has expanded the ECL versatility for detecting varying levels of dsDNA or ssDNA in plants with high sensitivity.

Interface-regulated S-type core-shell PCN-224@TiO2 heterojunction for visible-light-driven generation of singlet oxygen for selective photooxidation of 2-chloroethyl ethyl sulfide

Selective oxidation of sulfur mustard gas (HD) to non-toxic sulfoxide by the visible-light-catalyzed generation of singlet oxygen (1O2) is a promising degradation strategy. Although PCN-224 can absorb visible light, it suffers from rapid electron-hole recombination and low redox capacity, which limits the performance of HD degradation. Titanium dioxide (TiO2) is an excellent photocatalyst but it lacks visible-light-activity in degrading HD. In this study, PCN-224@TiO2 heterojunction with S-type core-shell structure was synthesized by in-situ growth method to prolong the visible light absorption capacity of TiO2 and inhibit the rapid recombination of PCN-224. The interface formation and internal electric field were optimized by adjusting the Zr/Ti ratio to enhance the charge transfer, redox capacity, electron-hole separation, and visible light absorption. In this study, the formation of heterojunction composites based on Zr-O-Ti linkages is demonstrated by a series of characterization methods. It is demonstrated by experiments and theoretical calculations that PCN-224@TiO2 can generate nearly 100 % 1O2 under visible light conditions without a sacrificial agent, resulting in efficient and selective oxidation of 2-chloroethyl ethyl sulfide (CEES), a simulant of HD, to non-toxic sulfoxide form.

Zr-based multivariate metal-organic framework for rapid extraction of sulfonamide antibiotics from water and food samples

Based on multiple ligands strategy, a series of multivariate metal organic frameworks (MTV-MOFs) named as PCN-224-DCDPSx were prepared using one-pot solvothermal method to extract and remove sulfonamide antibiotics (SAs). The pore structure and adsorption performance can be further regulated by modulating the doping ratios of medium-tetra(4-carboxylphenyl) porphyrin and 4,4'-dicarboxydiphenyl sulfones. The MTV-MOFs of PCN-224-DCDPS1.0 possesses very large specific surface area (1625 m2/g). Using PCN-224-DCDPS1.0 as sorbent, a dispersive solid-phase extraction method was developed to extract and preconcentrate SAs from water, eggs, and milk prior to high performance liquid chromatography analysis. The limits of detection of method were determined between 0.17 and 0.27 ng/mL with enrichment factors ranging 214-327. The adsorption can be finished within 30 s, and the recovery rate remains above 80 % after 10 repeated uses. The adsorption capacities of sorbent were determined from 300 to 621 mg/g for sulfadiazine, sulphapyridine, sulfamethoxydiazine, sulfachlorpyridazine, sulfabenzamide, and sulfadimethoxine. The adsorption mechanisms were investigated and can be attributed to π-π interactions, hydrogen bonds, and electrostatic interactions. This work represents a method for preparation of MTV-MOFs and uses as sorbent for extraction and enrichment of trace pollutants from complex samples.

Fine tuning of porphyrin based-paddlewheel framework by imidazole derivative to boost electrochemiluminescence performance

Precise tuning the structure of catalytic center is of great importance for the construction of enhanced electrochemiluminescence (ECL) emitters and the development of ECL amplification strategies, which is a key factor in improving the sensitivity of biosensors. In this work, we report the enhanced ECL emitters based on the porphyrin-based paddlewheel framework (PPF) with axial coordinated imidazole-like ligands (PPF/X, X = 2-methylimidazole (MeIm), imidazole (Im), benzimidazole (BIM)). In this system, the electron-donating ability of the axial ligands is positively correlated to its coordination ability to the paddlewheel units and the catalytic ability of the axially coordinated paddlewheel units. In addition, the electrochemical and ECL behavior of PPF/X (X = MeIm, Im, BIM) with different axial coordinated ligands are explored.

A portable transistor immunosensor for fast identification of porcine epidemic diarrhea virus

Widespread distribution of porcine epidemic diarrhea virus (PEDV) has led to catastrophic losses to the global pig farming industry. As a result, there is an urgent need for rapid, sensitive and accurate tests for PEDV to enable timely and effective interventions. In the present study, we develop and validate a floating gate carbon nanotubes field-effect transistor (FG CNT-FET)-based portable immunosensor for rapid identification of PEDV in a sensitive and accurate manner. To improve the affinity, a unique PEDV spike protein-specific monoclonal antibody is prepared by purification, and subsequently modified on FG CNT-FET sensor to recognize PEDV. The developed FET biosensor enables highly sensitive detection (LoD: 8.1 fg/mL and 100.14 TCID50/mL for recombinant spike proteins and PEDV, respectively), as well as satisfactory specificity. Notably, an integrated portable platform consisting of a pluggable FG CNT-FET chip and a portable device can discriminate PEDV positive from negative samples and even identify PEDV and porcine deltacoronavirus within 1 min with 100% accuracy. The portable sensing platform offers the capability to quickly, sensitively and accurately identify PEDV, which further points to a possibility of point of care (POC) applications of large-scale surveillance in pig breeding facilities.

Efficient porphyrin integrated UiO-66 probes for ratiometric fluorescence sensing of antibiotic residues in milk

Dual-emissive fluorescence probes were designed by integrating porphyrin into the frameworks of UiO-66 for ratiometric fluorescence sensing of amoxicillin (AMX). Porphyrin integrated UiO-66 showed dual emission in the blue and red region. AMX resulted in the quenching of blue fluorescence component, attributable to the charge neutralization and hydrogen bonds induced energy transfer. AMX was detected using (F438/F654) as output signals. Two linear relationships were observed (from 10 to 1000 nM and 1 to 100 µM), with a limit of detection of 27 nM. The porphyrin integrated UiO-66 probe was used to detect AMX in practical samples. This work widens the road for the development of dual/multiple emissive fluorescence sensors for analytical applications, providing materials and theoretical supporting for food, environmental, and human safety.

Recent Advances in Electrochemiluminescence Biosensors for MicroRNA Detection

Electrochemiluminescence (ECL) as an analytical technology with a perfect combination of electrochemistry and spectroscopy has received considerable attention in bioanalysis due to its high sensitivity and broad dynamic range. Given the selectivity of bio-recognition elements and the high sensitivity of the ECL analysis technique, ECL biosensors are powerful platforms for the sensitive detection of biomarkers, achieving the accurate prognosis and diagnosis of diseases. MicroRNAs (miRNAs) are crucial biomarkers involved in a variety of physiological and pathological processes, whose aberrant expression is often related to serious diseases, especially cancers. ECL biosensors can fulfill the highly sensitive and selective requirements for accurate miRNA detection, prompting this review. The ECL mechanisms are initially introduced and subsequently categorize the ECL biosensors for miRNA detection in terms of the quenching agents. Furthermore, the work highlights the signal amplification strategies for enhancing ECL signal to improve the sensitivity of miRNA detection and finally concludes by looking at the challenges and opportunities in ECL biosensors for miRNA detection.

A one-step immunoassay based on switching peptides for diagnosis of porcine epidemic diarrhea virus (PEDV) using screened Fv-antibodies

In this study, a one-step immunoassay for porcine epidemic diarrhea virus (PEDV) based on Fv-antibodies and switching peptides was developed, and the assay results of PEDV were obtained by just mixing samples without any further reaction or washing steps. The Fv-antibodies with binding affinity to the spike protein of PEDV were screened from the Fv-antibody library using the receptor-binding domain (RBD) of the spike protein as a screening probe. Screened Fv-antibodies with binding affinities to the RBD antigen were expressed, and the binding constants (KD) were calculated to be 83-142 nM. The one-step immunoassay for the detection of PEDV was configured as a displacement immunoassay using a fluorescence-labeled switching peptide. The one-step immunoassay based on switching peptides was performed using PEDV, and the limit of detection (LOD) values for PEDV detection were estimated to be Ct = 39.7-36.4. Compared with the LOD value for a conventional lateral flow immunoassay (Ct = 33.0), the one-step immunoassay showed a remarkably improved LOD for the detection of PEDV. Finally, the interaction between the screened Fv-antibodies and the PEDV RBD was investigated using docking simulations and compared with the amino acid sequences of the receptors on host cells, such as aminopeptidase N (APN) and angiotensin-converting enzyme-2 (ACE-2).

Dual-Signal Imaging Mode Based on Fluorescence and Electrochemiluminescence for Ultrasensitive Visualization of SARS-CoV-2 Spike Protein

Accurate and reliable detection of SARS-CoV-2 is critical for the effective prevention and rapid containment of COVID-19. Current approaches suffer from complex procedures or a single signal readout, resulting in an increased risk of false negatives and low sensitivity. Here, we developed a fluorescence (FL) and electrochemiluminescence (ECL) dual-mode imaging platform based on a self-powered DNAzyme walker to achieve accurate surveillance of SARS-CoV-2 spike protein at the single-molecule level. The specific activation of the DNAzyme walker by the target protein provides the power for the system's continuous running, enabling the simultaneous recording of the reduction in fluorescence spots and the appearance of ECL spots generated by the Ru-doped metal-organic framework (MOF) emitter. Therefore, the constructed imaging platform can achieve dual-mode detection of spike protein via reverse dual-signal feedback, which could effectively eliminate false-positive or false-negative signals and improve the detection accuracy and sensitivity with a low detection limit. In particular, the dual-mode accuracy of spike protein diagnosis in samples has been significantly improved compared to single-signal output means. In addition, this dual-mode imaging platform may become a prospective diagnostic device for other infectious viruses.

Antenna effect of perylene-sensitized up-conversion luminescent material amplifies the signal of electrochemiluminescence biosensor platform for the ultra-sensitive detection of enrofloxacin

Recently, up-conversion luminescent (UCL) materials have caught extensive sight on account of their excellent biocompatibility and weak automatic fluorescence background, but the low optical signal makes researchers shy away. Organic dye-sensitized UCL materials can improve the low optical signal drawback of UCL and rejuvenate it with adjustable optical properties and unique antenna effects. In this work, an efficient, simple and selective electrochemiluminescence (ECL) sensing platform was developed for determination of enrofloxacin (ENR). 3,4,9,10-perylene tetracarboxylic acid (PTCA) was successfully used as an "antenna" to improve the ECL performance of the UCL nanoparticles (PEI-NaYF4: Yb, Er) due to its appropriate excitation spectrum position and superior electron transfer rate. The specific recognition function of the aptamer enabled the sensor to eliminate the interference from conspecific impurity. In the presence of ENR, the specific combination of ENR with aptamer made the aptamer fall from surface of the electrode, thus we could see a considerable enhancement of signal. Under the most favourable conditions, the aptasensor based on antenna effect displayed a wide detection range (1.0 × 10-14∼1.0 × 10-6 M), low limit of detection (LOD = 3.0 × 10-15 M) and receivable recoveries (96.0%-102.4%) during water samples analysis. At this point, antenna effect provides a powerful strategy to expand the application of UCL in the field of ECL biosensing.

Enhancing the Electrochemiluminescence of Porphyrin via Crystalline Networks of Metal-Organic Frameworks for Sensitive Detection of Cardiac Troponin I

Porphyrins easily aggregate due to unfavorable π-π accumulation, causing luminescent quenching in the aqueous phase and subsequently reducing luminescent efficiency. It is a feasible way to immobilize porphyrin molecules through metal-organic framework materials (MOFs). In this study, 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin (TCPP) was introduced into the metal-organic skeleton (PCN-224) as a ligand. The result showed that the electrochemiluminescence (ECL) and photoluminescence (PL) efficiency of the MOF skeleton was 8.2 and 6.5 times higher than TCPP, respectively. Impressively, the periodic distribution of porphyrin molecules in the MOF framework can overcome the bottleneck of porphyrin aggregation, resulting in the organic ligand TCPP participating in the electron transfer reaction. Herein, based on the PCN-224, a sandwich-type ECL immunosensor was constructed for the determination of cardiac troponin I (cTnI). It provided sensitive detection of cTnI in the range of 1 fg/mL to 10 ng/mL with a detection limit of 0.34 fg/mL. This work not only innovatively exploited a disaggregation ECL (DIECL) strategy via the crystalline framework of MOF to enhance the PL and ECL efficiency of porphyrin but also provided a promising ECL platform for the ultrasensitive monitoring of cTnI.

Atomically Fe-anchored MOF-on-MOF nanozyme with differential signal amplification for ultrasensitive cathodic electrochemiluminescence immunoassay

The successful application of electrochemiluminescence (ECL) in immunoassays for clinical diagnosis requires stable electrodes and high-efficient ECL signal amplification strategies. Herein, the authors discovered a new class of atomically dispersed peroxidase-like nanozymes with multiple active sites (CoNi-MOF@PCN-224/Fe), which significantly improved the catalytic performance and uncovered the underlying mechanism. Experimental studies and theoretical calculation results revealed that the nanozyme introduced a Fenton-like reaction into the catalytic system and the crucial synergistic effects of definite active moieties endow CoNi-MOF@PCN-224/Fe strong electron-withdrawing effect and low thermodynamic activation energy toward H2O2. Benefiting from the high peroxidase-like activity of the hybrid system, the resultant ECL electrode exhibited superior catalytic activity in the luminol-H2O2 system and resulted in an ≈17-fold increase in the ECL intensity. In addition, plasmonic Ag/Au core-satellite nanocubes (Ag/AuNCs) were designed as high-efficient co-reactant quenchers to improve the performance of the ECL immunoassay. On the basis of the differential signal amplification strategy (DSAS) proposed, the immunoassay displayed superior detection ability, with a low limit of detection (LOD) of 0.13 pg mL-1 for prostate-specific antigen (PSA). The designed atomically anchored MOF-on-MOF nanozyme and DSAS strategy provides more possibilities for the ultrasensitive detection of disease markers in clinical diagnosis.

Allosteric probe-triggered isothermal amplification to activate CRISPR/Cas12a for sensitive electrochemiluminescence detection of Salmonella

We report an electrochemiluminescence (ECL) sensor for Salmonella detection based on allosteric probe as a bio-recognition element and CRISPR/Cas12a as a signal amplification strategy. In the presence of Salmonella, the structure switching occurs on allosteric probes, resulting in their hybridization with primers to trigger isothermal amplification. Salmonella is then released to initiate the next reaction cycle accompanying by generating a large amount of dsDNA, which are subsequently recognized by CRISPR-gRNA for activating the trans-cleavage activity of Cas12a. Furthermore, the activated Cas12a can indiscriminately cut the ssDNA which is bound to the electrode, enabling the release of the ECL emitter porphyrinic Zr metal - organic framework (MOF, PCN-224) and exhibiting a decreased ECL signal accordingly. The linear range is 50 CFU·mL^-1-5 × 10⁶ CFU·mL^-1 and the detection limit is calculated to be 37 CFU·mL^-1. This method sensitively detects Salmonella in different types of real samples, indicating it is a promising strategy for Salmonella detection.

Multifunctional Photoelectrochemical Biosensor Based on ZnIn2S4/ZnS QDs@Au-Ag-Reversed Photocurrent of Cu-Metal-Organic Framework Coupled with CRISPR/Cas-12a-Shearing for Assay of Dual Targets

False positives and negatives in bioanalytical assays remain a persistent problem. Herein, a multifunctional photoelectrochemical (PEC) biosensor based on ZnIn₂S₄ (ZIS)/ZnS quantum dots (QDs)@Au-Ag-reversed photocurrent of Cu-metal-organic framework (MOF) coupled with CRISPR/Cas-12a-shearing was innovatively developed for assay of dual targets. First, Cu-MOF as a good PEC material shows cathodic photocurrent. Then, numerous ZIS/ZnS QDs were assembled to the Au-Ag nanoparticles (NPs) to prepare a stable and highly amplified signal probe, which can just match the energy level of Cu-MOFs and realized the polarity-reversed photocurrent of Cu-MOF for the first time. As the empty-core nanostructure of Au-Ag NPs has a high specific surface area and low material density, the bimetallic nanocrystal can much increase the reaction rate and improve the redox efficiency. When target CEA-produced cDNA opened the hairpin DNA (HP1 DNA) on the electrode, the ZIS/ZnS QDs@Au-Ag signal probe was conjugated to the electrode via DNA hybridization, achieving a significantly reversed PEC current for CEA detection. Moreover, the specific binding of kanamycin/aptamer generated the acDNA (activator), which can activate the trans-cleavage activity of the CRISPR-CAS12a system on ssDNA, so the signal probe was sheared and caused the obvious decrease of PEC signal for kanamycin detection. The newly developed ZIS/ZnS QDs@Au-Ag NPs displayed excellent PEC properties and reversed photocurrent to MOF and were combined with the unique CRISPR-Cas12a system to achieve sensitive detection of dual targets, which can open a new polarity-reversed PEC sensing platform for rapid and accurate analysis of multiple targets and can effectively avoid false positives results in clinical testing.

An electrochemiluminescence aptasensor based on highly luminescent silver-based MOF and biotin-streptavidin system for mercury ion detection

In this study, for the first time, a silver-based metal-organic framework (Ag-MOF) was synthesized and used as the electrochemiluminescence (ECL) emitter for building an ECL sensor. After modification with chitosan (CS) and gold nanoparticles (Au NPs), the ECL stability of Ag-MOF was improved. To detect mercury ions, a biosensor was constructed using the mercury ion aptamer and steric effect of streptavidin. First, the capture strand (cDNA) with terminal-modified sulfhydryl group was attached to the electrode surface by the Au-S bond. Then, the mercury-ion aptamer (Apt-Hg) modified with biotin was anchored to the electrode by complementary pairing with cDNA. Streptavidin (SA) could be fixed on the electrode by linking with biotin, thereby reducing the ECL signal. However, in the presence of mercury ions, the aptamer was removed and streptavidin could not be immobilized on the electrode. Hence, the ECL signal of the sensor increased with the concentration of mercury ions, which was linear in the range from 1 μM to 300 fM. The detection limit could reach 66 fM (S/N = 3). The sensor provided a new method for the detection of mercury ions.

Cerium/polyacrylic acid modified porphyrin metal-organic framework as fluorescence and photothermal sensor for ascorbic acid measurement

A fluorescence and photothermal dual-signal assay was developed for the determination of ascorbic acid (AA). Cerium/polyacrylic acid modified porphyrin metal-organic frameworks (PCN-224@PAA-Ce MOFs) exhibit oxidase-like activity and can effectively oxidize 3,3 ', 5,5 '-tetramethylbenzidine (TMB) from colorless substrates to blue substrates (oxTMB). The absorption spectrum of oxTMB overlaps with the emission spectrum of PCN-224@PAA-Ce, resulting in quenching of fluorescence emission of PCN-224@PAA-Ce. oxTMB, as an excellent photothermal agent, converts the optical signal into the thermal signal (temperature increasing) driven by 808 nm laser. In the presence of AA, the blue oxTMB was reduced to colorless TMB, which led to the fluorescence recovery of PCN-224@PAA-Ce and at the same time, the photothermal signal was changed with the temperature decreasing under the driving of 808 nm laser. The detection limits (LOD) of fluorescence/photothermal dual-mode AA sensor strategies were as low as 0.73 μM and 1.4 μM, respectively. Rapid analysis of ascorbic acid was accomplished with the present procedure, AA in vitamin C tablets and human serum samples were validated.

Electrochemiluminescence resonance energy transfer biosensing platform between g-C3N4 nanosheet and Ru-SiO2@FA for dual-wavelength ratiometric detection of SARS-CoV-2 RdRp gene

Rational detection of syndrome coronavirus 2 (SARS-CoV-2) is crucial to prevention, control, and treatment of disease. Herein, a dual-wavelength ratiometric electrochemiluminescence (ECL) biosensor based on resonance energy transfer (RET) between g-C₃N₄ nanosheets and Ru-SiO₂@folic acid (FA) nanomaterials was designed to realize ultrasensitive detection of SARS-CoV-2 virus (RdRp gene). Firstly, the unique g-C₃N₄ nanosheets displayed very intense and stable ECL at 460 nm, then the triple helix DNA was stably and vertically bound to g-C₃N₄ on electrode by high binding affinity between ssDNA and g-C₃N₄. Meanwhile, trace amounts of target genes were converted to a large number of output by three-dimensional (3D) DNA walker multiple amplification, and the output bridged a multifunctional probe Ru-SiO₂@FA to electrode. Ru-SiO₂@FA not only showed high ECL at 620 nm, but also effectively quenched g-C₃N₄ ECL. As a result, ECL decreased at 460 nm and increased at 620 nm, which was used to design a rational ECL biosensor for detection of SARS gene. The results show that the biosensor has excellent detection sensitivity for RdRp gene with a dynamic detection range of 1 fM to 10 nM and a limit of detection (LOD) of 0.18 fM. The dual-wavelength ratio ECL biosensor has inestimable value and application prospects in the fields of biosensing and clinical diagnosis.

Programmable Y-Shaped Probes with Proximity Bivalent Recognition for Rapid Electrochemiluminescence Response of Acute Myocardial Infarction

Herein, an exogenous luminophore-free and disposable electrochemiluminescence (ECL) biosensor was established for rapid response of acute myocardial infarction (AMI) using programmable Y-shaped probes (Y-probes) with proximity bivalent recognition. Specifically, the indium tin oxide thin film coated glass electrode (ITO) was modified with urchin-like porous TiO₂ microspheres (pTiO₂ MSs), which could achieve strong and stable ECL in S₂O₈^2- solution due to the dual promoting effect of the coreaction accelerator pTiO₂ MSs, exhibiting 2.7-fold higher ECL intensity in comparison with that of bare ITO. Moreover, the Y-probes as bivalent recognition elements containing two kinds of cardiac troponin I (cTnI, a biomarker of AMI) aptamers and a linker labeled with ferrocene (L-Fc) were designed to export a "signal off" mode. When the target cTnI was in the proximity of the Y-probes, the L-Fc was separated from the electrode surface due to the proximity recognition of cTnI and its aptamers, achieving the highly effective recovery of ECL, which allowed for a much more rapid detection of cTnI than the sandwich-type immunoassay. As a proof of concept, an exogenous luminophore-free and disposable ECL platform for rapid and sensitive monitoring of cTnI was obtained and displayed a desired linear range from 100 fg mL^-1 to 100 ng mL^-1 with a limit of detection (LOD) of 30.1 fg mL^-1, which can be ingeniously expanded as a portable home tester with ECL biosensors developments.

Nanomaterials for virus sensing and tracking

The effect of the on-going COVID-19 pandemic on global healthcare systems has underlined the importance of timely and cost-effective point-of-care diagnosis of viruses. The need for ultrasensitive easy-to-use platforms has culminated in an increased interest for rapid response equipment-free alternatives to conventional diagnostic methods such as polymerase chain reaction, western-blot assay, etc. Furthermore, the poor stability and the bleaching behavior of several contemporary fluorescent reporters is a major obstacle in understanding the mechanism of viral infection thus retarding drug screening and development. Owing to their extraordinary surface-to-volume ratio as well as their quantum confinement and charge transfer properties, nanomaterials are desirable additives to sensing and imaging systems to amplify their signal response as well as temporal resolution. Their large surface area promotes biomolecular integration as well as efficacious signal transduction. Due to their hole mobility, photostability, resistance to photobleaching, and intense brightness, nanomaterials have a considerable edge over organic dyes for single virus tracking. This paper reviews the state-of-the-art of combining carbon-allotrope, inorganic and organic-based nanomaterials with virus sensing and tracking methods, starting with the impact of human pathogenic viruses on the society. We address how different nanomaterials can be used in various virus sensing platforms (e.g. lab-on-a-chip, paper, and smartphone-based point-of-care systems) as well as in virus tracking applications. We discuss the enormous potential for the use of nanomaterials as simple, versatile, and affordable tools for detecting and tracing viruses infectious to humans, animals, plants as well as bacteria. We present latest examples in this direction by emphasizing major advantages and limitations.

Bioactive hybrid metal-organic framework (MOF)-based nanosensors for optical detection of recombinant SARS-CoV-2 spike antigen

Fast, efficient, and accurate detection of SARS-CoV-2 spike antigen is pivotal to control the spread and reduce the mortality of COVID-19. Nevertheless, the sensitivity of available nanobiosensors to detect recombinant SARS-CoV-2 spike antigen seems insufficient. As a proof-of-concept, MOF-5/CoNi₂S₄ is developed as a low-cost, safe, and bioactive hybrid nanostructure via the one-pot high-gravity protocol. Then, the porphyrin, H₂TMP, was attached to the surface of the synthesized nanomaterial to increase the porosity for efficient detection of recombinant SARS-CoV-2 spike antigen. AFM results approved roughness in different ranges, including 0.54 to 0.74 μm and 0.78 to ≈0.80 μm, showing good physical interactions with the recombinant SARS-CoV-2 spike antigen. MTT assay was performed and compared to the conventional synthesis methods, including hydrothermal, solvothermal, and microwave-assisted methods. The synthesized nanodevices demonstrated above 88% relative cell viability after 24 h and even 48 h of treatment. Besides, the ability of the synthesized nanomaterials to detect the recombinant SARS-CoV-2 spike antigen was investigated, with a detection limit of 5 nM. The in-situ synthesized nanoplatforms exhibited low cytotoxicity, high biocompatibility, and appropriate tunability. The fabricated nanosystems seem promising for future surveys as potential platforms to be integrated into biosensors.

Electrochemiluminescent sensor based on an aggregation-induced emission probe for bioanalytical detection

In recent years, with the rapid development of electrochemiluminescence (ECL) sensors, more luminophores have been designed to achieve high-throughput and reliable analysis. Impressively, after the proposed fantastic concept of "aggregation-induced electrochemiluminescence (AIECL)" by Cola, the application of AIECL emitters provides more abundant choices for the further improvement of ECL sensors. In this review, we briefly report the phenomenon, principle and representative applications of aggregation-induced emission (AIE) and AIECL emitters. Moreover, it is noteworthy that the cases of AIECL sensors for bioanalytical detection are summarized in detail, from 2017 to now. Finally, inspired by the applications of AIECL emitters, relevant prospects and challenges for AIECL sensors are proposed, which is of great significance for exploring more advanced bioanalytical detection technology.

Novel CdS/MOF Cathodic Photoelectrochemical (PEC) Platform for the Detection of Doxorubicin Hydrochloride and Gentamicin Sulfate

Nanomaterial selection is critical for photoelectrochemical (PEC) sensing. In this report, a novel cathodic photoelectrochemical (PEC) strategy was proposed for the detection of doxorubicin hydrochloride (Dox) and gentamicin sulfate (CN). The photocathode was synthesized by noncovalently coupling cadmium sulfide (CdS) to the porphyrin-derived metal-organic framework (CdS@PCN-224). This type of assembly created a pleasant interface for the combination of doxorubicin hydrochloride and gentamicin sulfate, resulting in a good CdS@PCN-224 donor-acceptor system. When compared to a single optoelectronic material, its photocurrent is enhanced by unprecedented nine times. This research could pave the way for the realization of PCN-224's enormous potential in PEC sensing.

Direct electrochemistry of silver nanoparticles-decorated metal-organic frameworks for telomerase activity sensing via allosteric activation of an aptamer hairpin

A direct electrochemistry of silver nanoparticles (AgNPs)-anchored metal-organic frameworks (MOFs) is developed for detection of telomerase activity based on allosteric activation of an aptamer hairpin. AgNPs in situ decorated on PCN-224 (AgNPs/PCN-224) constituted the direct electrochemical labels that were further biofunctionalized by recognition moiety of streptavidin (SA). To achieve the target biosensing, an allosteric hairpin-structured DNA was elaborately designed for signal transduction. The presence of telomerase elongated its primer in the hairpin to displace partial stem strand, thus resulted in the formation of SA aptamer-open structure. Through the specific interaction with aptamer, SA-biofunctionalized AgNPs/PCN-224 probe was attached onto the electrode surface, generating electrochemical signal at + 0.072 V of AgNPs centralized by MOF structure. The direct electrochemical biosensor showed target activity-dependent response from 1.0 × 10^-7 to 1.0 × 10^-1 IU L^-1 with a detection limit of 5.4 × 10^-8 IU L^-1. Moreover, the sensor was applied in evaluation of telomerase activity in living cancer cells. The established electrochemical detection approach in this work avoids the critical deoxygenation conditions and additional electrocatalytic reagents, which opens a novel biosensing perspective for direct electrochemistry of MOF-based nanocomposites.

Ultrasensitive ECL aptasensing of kanamycin based on synergistic promotion strategy using 3,4,9,10-perylenetetracar-boxylic-l-cysteine/Au@HKUST-1

Herein, a sensitive and selective electrochemiluminescence (ECL) aptasensor was designed using Au@HKUST-1 as accelerator towards the perylene derivative (PTC-Cys)/peroxydisulfate (S₂O₈^2-) system for kanamycin (KAN) assay. Firstly, the PTC-Cys was prepared by covalently binding l-cysteine to 3,4,9,10-perylenete-tracarboxylic acid, which was acted as the luminophore. Then Au@HKUST-1could play the part of effective catalyst to accelerate the electrochemical reduction process of S₂O₈^2-to produce more sulfate radical anions (SO₄^•-), thus the ECL signal of the compound was noticeably raised by 2.4 times in comparison with that in which only luminophore and S₂O₈^2- are present, achieving signal amplification of the ECL system. In the presence of KAN, aptamer was pulled down from the sensing interface, achieving a considerable enhancement of ECL intensity in S₂O₈^2- solution. Upon the optimal condition, our proposed strategy can quantify the concentration of KAN from 1.0 × 10^-13 to 1.0 × 10^-8 M with low limit of detection of 4.2 × 10^-14 M (S/N = 3).Besides, our proposed ECL aptasensor exhibited excellent sensitivity, stability and specificity, and could be successfully applied to detect KAN in practical samples, which proved its potential to detect other antibiotics in food security.

Functionalized europium-porphyrin coordination polymer: Rational design of high performance electrochemiluminescence emitter for mucin 1 sensing

The excellent characteristics of porphyrins have inspired widespread interest in electrochemiluminescence (ECL). However, the limited ECL intensity and poor stability of porphyrins in aqueous solution are still severely restricted further biological application. Here, we subtly synthesized a functionalized europium and 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin (TCPP) coordination polymer (Eu-PCP) by a one-step solvothermal method. In sharp contrast to the pristine TCPP, Eu-PCP showed a higher and more stable ECL red-light emission (673 nm) at low potential (-1.1 V, vs Ag/AgCl), which was 7.7-fold higher ECL intensity and 4.6-fold efficiency. In view of the crucial role of mucin 1 (MUC1) in tumor overexpression, it was selected as the target molecule. Combined with exonuclease III (Exo III)-assisted recycling amplification strategy, a ternary ECL biosensor was constructed for the MUC1 detection based on Eu-PCP as a satisfied ECL emitter, gold nanoparticles capped CeO₂ (CeO₂@Au) as the coreactant accelerator and peroxydisulfate as coreactant. Meanwhile, gold nanoparticles capped MnO₂ (MnO₂@Au) was used as the quenching probe to achieve a highly sensitive detection of MUC1. The proposed biosensor exhibited a wide linear range from 1 fg mL^-1 to 10 ng mL^-1 with a low limit of detection (0.32 fg mL^-1). By changing the corresponding target recognition DNA, this strategy could be expanded to detect other biomarkers.