Ferritin-Based Electrochemiluminescence Nanosurface Energy Transfer System for Procalcitonin Detection Using HWRGWVC Heptapeptide for Site-Oriented Antibody Immobilization

Dual-signaling and ultrasensitive detection for PCT based on the photoelectric and electrocatalytic hydrogen evolution signals of Pt/Mo-CoFeS

Few study has been carried out on the construction of immunesensors utilized the photoelectric and catalytic signal of nanomaterial. Here, a dual-signal electrochemical immunosensor was constructed for procalcitonin (PCT) detection based on the excellent photoelectric and hydrogen evolution performance of molybdenum-doped cobalt-iron sulfur nanosheets modified by platinum nanoparticles (Pt/Mo-CoFeS). Due to the electronic structure regulation between Pt and Mo-CoFeS, Pt/Mo-CoFeS exhibits superior photoelectric and hydrogen evolution performance compared to single Mo-CoFeS, which improved the sensitivity of the electrochemical immunosensor. Furthermore, the presence of Pt improves surface area and biocompatibility, achieving more antibodies loading and signal amplification. The linear range of PCT detection are 0.002-20 ng mL-1 and 0.002-50 ng mL-1, the detection limits are 0.0015 and 0.0012 ng mL-1. In addition, this electrochemical immunosensor was applied to the PCT analysis in human serum samples with high recoveries. F-test and t-test show that there is no significant difference in the test results between the HER and photoelectric signals, the mutual verification between above two signals can effectively improve the accuracy of detection result.

Systematic review and meta-analysis of human health-related protein markers for realizing real-time wastewater-based epidemiology

For effective implementation of the wastewater-based epidemiology (WBE) approach, real-time quantification of markers in wastewater is critical for data acquisition before data interpretation, dissemination, and decision-making. This can be achieved by using biosensor technology, but whether the quantification/detection limits of different types of biosensors comply with the concentration of WBE markers in wastewater is unclear. In the present study, we identified promising protein markers with relatively high concentrations in wastewater samples and analyzed biosensor technologies that are potentially available for real-time WBE. The concentrations of potential protein markers in stool and urine samples were obtained through systematic review and meta-analysis. We examined 231 peer-review papers to collect information regarding potential protein markers that can enable us to achieve real-time monitoring using biosensor technology. Fourteen markers in stool samples were identified at the ng/g level, presumably equivalent to ng/L of wastewater after dilution. Moreover, relatively high average concentrations of fecal inflammatory proteins were observed, e.g., fecal calprotectin, clusterin, and lactoferrin. Fecal calprotectin exhibited the highest average log concentration among the markers identified in stool samples with its mean value being 5.24 [95 % CI: 5.05, 5.42] ng/g. We identified 50 protein markers in urine samples at the ng/mL level. Uromodulin (4.48 [95 % CI: 4.20, 4.76] ng/mL) and plasmin (4.18 [95 % CI: 3.15, 5.21] ng/mL) had the top two highest log concentrations in urine samples. Furthermore, the quantification limit of some electrochemical- and optical-based biosensors was found to be around the femtogram/mL level, which is sufficiently low to detect protein markers in wastewater even after dilution in sewer pipes.

Materials for Electrochemiluminescence: TADF, Hydrogen-Bonding, and Aggregation- and Crystallization-Induced Emission Luminophores

Electrochemiluminescence (ECL) is a rapidly growing discipline with many analytical applications from immunoassays to single-molecule detection. At the forefront of ECL research is materials chemistry, which looks at engineering new materials and compounds exhibiting enhanced ECL efficiencies compared to conventional fluorescent materials. In this review, we summarize recent molecular design strategies that lead to high efficiency ECL. In particular, we feature recent advances in the use of thermally activated delayed fluorescence (TADF) emitters to produce enhanced electrochemiluminescence. We also document how hydrogen bonding, aggregation, and crystallization can each be recruited in the design of materials showing enhanced electrochemiluminescence.

Intramolecular Enhancement of a Zirconium-Based Metal-Organic Framework for Coordination-Induced Electrochemiluminescence Bleomycin Analysis

It is significantly vital to develop a convenient assay method in clinical treatment due to an atypically low abundance (∼5 μM) of bleomycin (BLM) used in clinics. Herein, an electrochemiluminescence (ECL) biosensor using a zirconium-based metal-organic frameworks (Zr-MOFs) as an intramolecular coordination-induced electrochemiluminescence (CIECL) emitter was proposed for sensitive detection of BLM. Zr-MOFs were synthesized using Zr(IV) as metal ions and 4,4',4″-nitrilotribenzoic acid (H₃NTB) as ligands for the first time. The H₃NTB ligand not only acts as coordination units bonding with Zr(IV) but functions as a coreactant to enhance ECL efficiency rooted in its tertiary nitrogen atoms. Specifically, a long guanine-rich (G-rich) single-stranded DNA (ssDNA) was released by the target-BLM-controlled DNA machine that could perform π-π stacking with another G-quadruplex, ssDNA-rhodamine B (S-RB), by shearing DNA's fixed sites 5'-GC-3' and the auxiliary role of exonuclease III (Exo III). Finally, due to the quenching effect of rhodamine B, a negative correlation trend was obtained between ECL intensity and BLM concentration in the range from 5.0 nM to 50 μM and the limit of detection was 0.50 nM. We believe that it is a promising approach to guide the preparation of CIECL-based functional materials and establishment of analytical methods.

Recent advances and challenges in developing electrochemiluminescence biosensors for health analysis

This Feature Article simply introduces principles and mechanisms of electrochemiluminescence (ECL) biosensors for the determination of biomarkers and highlights recent advances of ECL biosensors on key aspects including new ECL reagents and materials, new biological recognition elements, and emerging construction biointerfacial strategies with illustrative examples and a critical eye on pitfalls and discusses challenges and perspectives of ECL biosensors for health analysis.

Hydrogen Bond Organic Frameworks as Radical Reactors for Enhancement in ECL Efficiency and Their Ultrasensitive Biosensing

Nowadays, electrochemiluminescence (ECL) efficiency of an organic emitter is closely related with its potential applications in food safety and environmental monitoring fields. In this work, 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine (TATB) was self-assembled to form hydrogen bond organic frameworks (HOFs), which worked as ideal reactors to generate highly active oxygen-containing radicals, followed by linking with isoluminol (ILu) via amide bond (termed ILu-HOFs). After covalent assembly with aminated indium-tin oxide electrode (labeled NH₂-ITO), the ECL efficiency of the ILu-HOFs NH₂-ITO showed about a 23.4-time increase over that of ILu itself in the presence of H₂O₂. Meanwhile, the enhanced ECL mechanism was mainly studied by electron paramagnetic resonance, theoretical calculation, and electrochemistry. On the above foundation, an aptamer "sandwich" ECL biosensor was constructed for detecting isocarbophos (ICP) via in situ elimination of H₂O₂ with catalase-linked palladium nanocubes (CAT-Pd NCs). The as-built sensor showed a broad linear range (1 pM to 100 nM) and a low limit of detection (LOD) down to 0.4 pM, coupled with efficient assays of ICP in lake water and cucumber juice samples. This strategy provides an effective way for the synthesis of advanced ECL emitter, coupled by showing promising applications in environmental and food analysis.

Coreactant-free electrochemiluminescence of polyfluorene nanoparticle coupling double quencher for β-amyloid1-42 detection

β-amyloid_1-42 (Aβ_1-42) is a humoral biomarker for early diagnosis of Alzheimer's disease (AD), and exists at a low level in human body. Its sensitive detection is very valuable. The electrochemiluminescence (ECL) assay of Aβ_1-42 has attracted special attention owing to high sensitivity and simple operation. However, currently reported ECL assays for Aβ_1-42 usually required the introduction of exogenous coreactants to improve the detection sensitivity. Introducing exogenous coreactants will lead to non-negligible repeatability and stability problems. This work exploited poly [(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadazole)] nanoparticles (PFBT NPs) as coreactant-free ECL emitters for detecting Aβ_1-42. The PFBT NPs, first antibody (Ab₁) and antigen Aβ_1-42 were successively assembled on glassy carbon electrode (GCE). Silica nanoparticles served as a carrier to grow polydopamine (PDA) in situ, and further assembled Au nanoparticles (Au NPs) and second antibody (Ab₂), producing the secondary antibody complex (SiO₂@PDA-Au NPs-Ab₂). With its assembly on the biosensor, the ECL signal decreased since both PDA and Au NPs could quench ECL emission from PFBT NPs. The limit of detection (LOD) of 0.55 fg/mL and limit of quantification (LOQ) of 37.45 fg/mL for Aβ_1-42 were obtained. PFBT NPs coupling dual-quencher PDA-Au NPs created an excellent ECL system for bioassays, and constructed a sensitive analytical method for Aβ_1-42.

Electrochemiluminescence nanoemitters for immunoassay of protein biomarkers

The family of electrochemiluminescent luminophores has witnessed quick development since the electrochemiluminescence (ECL) phenomenon of silicon nanoparticles was first reported in 2002. Moreover, these developed ECL nanoemitters have extensively been applied in sensitive detection of protein biomarker by combining with immunological recognition. This review firstly summarized the origin and development of various ECL nanoemitters including inorganic and organic nanomaterials, with an emphasis on metal-organic frameworks (MOFs)-based ECL nanoemitters. Several effective strategies to amplify the ECL response of nanoemitters and improve the sensitivity of immunosensing were discussed. The application of ECL nanoemitters in immunoassay of protein biomarkers for diagnosis of cancers and other diseases, especially lung cancer and heart diseases, was comprehensively presented. The recent development of ECL imaging with the nanoemitters as ECL tags for detection of multiplex protein biomarkers on single cell membrane also attracted attention. Finally, the future opportunities and challenges in the ECL biosensing field were highlighted.

Cu2O@PdAg-quenched CdS@CeO2 heterostructure electrochemiluminescence immunosensor for determination of prostate-specific antigen

Based on the resonance energy transfer between CdS@CeO₂ and Cu₂O@PdAg, a quenching immunosensor for sensitive detection of prostate specific antigen (PSA) was constructed. The CdS@CeO₂ heterostructure was obtained by in situ growth of CeO₂ particles on the surface of CdS nanorods, and stable cathodic ECL emission was achieved using K₂S₂O₈ as coreactant. Cu₂O@PdAg was composed of Cu₂O with tetradecahedral structure and bimetallic PdAg nanospheres and has a UV-V is absorption range between 600 and 800 nm. It overlaps with the ECL emission spectrum of CdS@CeO₂, realizing the effective quenching of the ECL signal, which provides feasibility for subsequent practical application. The immunosensor exhibited good linearity in the concentration range 10 fg·mL^-1 ~ 100 ng·mL^-1, with a detection limit of 5.6 fg·mL^-1. In sample analysis, the recoveries were 99.8-101%, and the relative standard deviation (RSD) was 0.85-1.6% showing great potential and development value for the sensitive detection of prostate cancer.

Construction of efficient electrochemiluminescence resonance energy transfer sensor based on SnO2/SnS2QDs-Ru@IRMOF-3 composite for sensitive detection of procalcitonin

An efficient electrochemiluminescence resonance energy transfer (ECL-RET) method is proposed which combines the luminescent materials of tris(4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium(II) (energy donor) and tin dioxide and tin disulfide quantum dots (SnO₂/SnS₂QDs) (energy acceptor) into the isoreticular metal - organic framework-3 (IRMOF-3) material to form a composite. In this mode, the distance between the energy donor and the acceptor was greatly shortened, reducing the energy loss, and thereby effectively improving RET efficiency and further significantly improving the ECL signal. The obtained composite (SnO₂/SnS₂QDs-Ru@IRMOF-3) was combined with sandwich immunoreaction to construct an ECL immunosensor for the sensitive detection of procalcitonin (PCT). Under the optimized experimental conditions with a working potential of - 1.48 V (vs Ag/AgCl), the proposed PCT biosensor exhibited a linear concentration range of 1 × 10^-4-200 ng mL^-1, with a detection limit of 0.029 pg mL^-1 (S/N = 3). The biosensor was used to detect PCT in actual samples. The biosensor has broad application prospects in biological analysis and clinical diagnosis due to its high sensitivity, good selectivity, and good stability.

Detection of COVID-19-related biomarkers by electrochemical biosensors and potential for diagnosis, prognosis, and prediction of the course of the disease in the context of personalized medicine

As a more efficient and effective way to address disease diagnosis and intervention, cutting-edge technologies, devices, therapeutic approaches, and practices have emerged within the personalized medicine concept depending on the particular patient's biology and the molecular basis of the disease. Personalized medicine is expected to play a pivotal role in assessing disease risk or predicting response to treatment, understanding a person's health status, and, therefore, health care decision-making. This work discusses electrochemical biosensors for monitoring multiparametric biomarkers at different molecular levels and their potential to elucidate the health status of an individual in a personalized manner. In particular, and as an illustration, we discuss several aspects of the infection produced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as a current health care concern worldwide. This includes SARS-CoV-2 structure, mechanism of infection, biomarkers, and electrochemical biosensors most commonly explored for diagnostics, prognostics, and potentially assessing the risk of complications in patients in the context of personalized medicine. Finally, some concluding remarks and perspectives hint at the use of electrochemical biosensors in the frame of other cutting-edge converging/emerging technologies toward the inauguration of a new paradigm of personalized medicine.

Efficient ABEI-Dissolved O2-Ce(III, IV)-MOF Ternary Electrochemiluminescent System Combined with Self-Assembled Microfluidic Chips for Bioanalysis

A signal-amplified electrochemiluminescent (ECL) sensor chip was developed for sensitive analysis of procalcitonin (PCT). Herein, we first prepared a self-enhanced luminophore, which enhanced ECL responses through intramolecular reactions. Second, Au-Pd bimetallic nanocrystals and mixed-valence Ce-based metal-organic frameworks (MOFs) were introduced as co-reaction promoters to facilitate the reduction of dissolved O₂. Based on the synergistic catalysis of Au and Pd, the spontaneous cyclic reaction of Ce(III)/Ce(IV), and the high electrochemical active surface area of Ce(III, IV) MOF, a large number of superoxide anion radicals (O₂^•-) and hydroxyl radicals (OH^•) were produced. Therefore, the luminescence efficiency of N-(aminobutyl)-N-(ethylisoluminol)-dissolved O₂ (ABEI-O₂) systems were greatly improved, providing a new prospect for the application of dissolved O₂ in ECL analysis. In addition, the affinity peptide ligands were used for the directional connection of antibodies to provide protection for the bioactivity of the proposed sensor. Finally, the microfluidic technology was applied to ECL analysis to integrate the three-electrode detection system into the self-assembled microfluidic chip, which realized the automation and portability of the detection process. The developed sensor showed high sensitivity for PCT detection with a detection limit of 3.46 fg/mL, which possessed positive significance for the clinical diagnosis of sepsis.

Hollow Double-Shell CuCo2O4@Cu2O Heterostructures as a Highly Efficient Coreaction Accelerator for Amplifying NIR Electrochemiluminescence of Gold Nanoclusters in Immunoassay

The evolution of electrochemiluminescence (ECL) emission amplified by coreaction accelerator in near-infrared (NIR) area has been overwhelmingly anticipated for ultrasensitive detection of disease biomarkers. Herein, the hollow double-shell CuCo₂O₄@Cu₂O (HDS-CuCo₂O₄@Cu₂O) heterostructures were conveniently prepared and utilized as an attractive coreaction accelerator to improve the NIR ECL performance of gold nanoclusters (AuNCs) for the first time. Benefiting from perfect-matched lattice spacing, unique Cu₂O nanoparticles (NPs) were formed in situ on the layered-hollow CuCo₂O₄ nanospheres (NSs) to obtain HDS-CuCo₂O₄@Cu₂O heterostructures. The formed heterojunctions supplied shorter charge transfer distance and better interfacial charge transfer efficiency as well as more effective separation performance. Consequently, HDS-CuCo₂O₄@Cu₂O heterostructures as an admirable electroactive substrate could significantly promote the formation of sufficient coreactant intermediate radicals to react with AuNCs cationic radicals, realizing about 3-folds stronger NIR ECL response than that of individual AuNCs. In addition, the AuNCs templated by l-methionine (l-Met) exhibited NIR ECL emission around 830 nm, which could decrease the photochemical damage to even realize a nondestructive detection with improved susceptibility and circumambient adaptability. Subsequently, a well site-oriented fixation strategy utilizing HWRGWVC heptapeptide as the specific antibody immobilizer was introduced to further preserve the bioactivity of antibody on the HDS-CuCo₂O₄@Cu₂O and AuNCs surface along with enhancing the incubation performance markedly. In view of the progressive sensing mechanism, a NIR immunosensor was obtained for the ultrasensitive analysis of CYFRA21-1, which achieved a broad linear ranging from 2 fg/mL to 50 ng/mL and a low limit of detection (LOD) of 0.67 fg/mL (S/N = 3).

Characterization of a heptapeptide-modified microsphere for oriented antibody immobilization

Oriented immobilization of antibodies is important for the effective recognition of target antigens. In this paper, a heptapeptide ligand, HWRGWVC (HC7), was modified onto non-porous mono-sized poly (glyceryl methacrylate) (pGMA) microspheres (named pGMA-HC7) to explore the antibody immobilization behaviors. Characterization of the microspheres by particle size analyzer, scanning electron microscopy, Fourier transform infrared spectroscopy, and reversed-phase chromatography proved the success of each fabrication step. The capacity and activity of antibody immobilization through HC7 were studied using immunoglobulin G (IgG) as a model antibody and horseradish peroxidase (HRP) as a model antigen. Additionally, IgG immobilizations on pGMA microspheres by nonspecific adsorption and covalent coupling through carbodiimide chemistry were conducted for comparison. pGMA-HC7 exhibited an IgG adsorption capacity of 3-4 mg/g in 10 min by the specific binding of HC7 without nonspecific interactions. Notably, the ligand HC7 showed a by two orders of magnitude stronger affinity for IgG than its original hexapeptide ligand HWRGWV. Moreover, the capacity and activity of the immobilized anti-HRP antibody on pGMA-HC7 were 1.6-fold and 3-fold higher than those of the covalent coupling, respectively. The results proved the superior role of HWRGWVC in the affinity binding of antibody and the potential of pGMA-HC7-25 in immunoassay and immunodiagnostic applications.

A polypyrrole-mediated photothermal biosensor with a temperature and pressure dual readout for the detection of protein biomarkers

A novel photothermal biosensor with a temperature and pressure dual readout was developed for CRP detection. The in situ synthesized polypyrrole exhibits photothermal effect under NIR light to increase temperature and pressure for portable readout.

Sandwich-type photoelectrochemical immunosensor for procalcitonin detection based on Mn2+ doped CdS sensitized Bi2WO6 and signal amplification of NaYF4:Yb, Tm upconversion nanomaterial

In this paper, we constructed a sandwich-type photoelectrochemical (PEC) immunosensor for the quantitative detection of procalcitonin (PCT) based on the sensitization of Mn²⁺ doped CdS (CdS:Mn) nanocomposites to Bi₂WO₆ and the signal amplification effect of an upconversion material NaYF₄:Yb,Tm. Bi₂WO₆ was synthesized with a three-dimensional flowered structure. CdS:Mn reduced the recombination of photogenerated carriers, and significantly improved photocurrent response. Lanthanide-doped upconversion nanomaterials were used as the label of secondary antibody. NaYF₄:Yb,Tm have two functions, not only connected with the secondary antibody, but also can further amplify the photocurrent response. The proposed immunosensor for detecting PCT provided a desired linear range of 0.5 pg mL^-1-100 ng mL^-1 and a detection limit of 0.13 pg mL^-1 under optimal experimental conditions. Besides, the PEC immunosensor demonstrated good reproducibility, specificity and stability. The results of determination of PCT in real human serum samples were satisfactory. Thus, the immunosensor may be applied in the clinical diagnosis of PCT and other biomarkers.

A dual signal-amplified electrochemiluminescence immunosensor based on core-shell CeO2-Au@Pt nanosphere for procalcitonin detection

A dual signal-amplified sandwich electrochemiluminescence (ECL) immunosensor was fabricated for trace detection of procalcitonin (PCT). CeO₂-Au@Pt composed of sea urchin-like Au@Pt nanoparticles coated on CeO₂ hollow nanospheres was immobilized on electrode surface to electrochemically catalyze H₂O₂ to produce a large number of superoxide anion (O₂^•-). The immunosensor was prepared by linking the capture antibody on immobilized CeO₂-Au@Pt with heptapeptide (HWRGWVC), which could maintain the activity of the antibody. The prepared Au star@BSA was used to bind abundant luminol for labeling the secondary antibody (Ab₂). Upon the sandwich-typed immunoreactions, the O₂^•- could react with the introduced luminol on the immunosensor surface to produce strong ECL intensity. With an outstanding linear detection range and a low detection limit of 17 fg/mL, the ECL immunosensor permitted ultrasensitive detection of PCT at a low H₂O₂ concentration and demonstrated its high application potential in the clinical assay.

Rationally engineered high-performance BiVO4/Ag3VO4/SnS2 photoelectrodes for ultrasensitive immunosensing of CYFRA21-1 based on HRP-tyramine-triggered insoluble precipitates

A photoelectrochemical (PEC) biosensor capable of detecting cytokeratin 19 fragment 21-1 (CYFRA21-1) was optimized by taking advantage of the powerful conjugate repeats of horseradish peroxidase and tyramine (HRP-tyramine)-triggered enzymatic biocatalytic precipitation (BCP) on high-performance BiVO₄/Ag₃VO₄/SnS₂ photoelectrodes. Compared with the ubiquitous BCP strategy, we identified a design supporting conjugate repeats generated by HRP and tyramine-triggered immeasurable insoluble precipitates in the presence of hydrogen peroxide and 4-chloro-1-phenol (4-CN), and the steric hindrance improved sensitivity. Moreover, by virtue of BiVO₄, Ag₃VO₄, SnS₂ excellent level matching structure and chemical stability, a heterojunction (BiVO₄/Ag₃VO₄/SnS₂) with high light absorption efficiency has been successfully prepared. The novel heterostructure system of BiVO₄/Ag₃VO₄/SnS₂ with high detection current and low background signal exhibited high-performance PEC determination. Generally, the hitherto untapped biosensor resource realized the sensitive detection of CYFRA21-1 with a wide linear range from 50 fg/mL to 200 ng/mL, and a detection limit of 15 fg/mL, which illustrated the potential for biotechnological applications.

Facile construction of ratiometric electrochemical immunosensor using hierarchical PtCoIr nanowires and porous SiO2@Ag nanoparticles for accurate detection of septicemia biomarker

Procalcitonin (PCT) is a sensitive and specific biomarker for sepsis diagnosis. In this study, a novel ratio-typed electrochemical immunosensor was constructed for reliable and sensitive assay of PCT based on hierarchical PtCoIr nanowires/polyethylene polyamine-grafted-ferrocene (PtCoIr HNWs/PEPA-Fc) and porous SiO₂@Ag nanoparticles-toluidine blue (porous SiO₂@Ag NPs-TB). Importantly, the PtCoIr HNWs/PEPA-Fc was first modified on the sensing interface, which harvested stable and strong electrochemical signals for readout of Fc due to the enriched anchoring sites created by the PtCoIr HNWs. Meanwhile, porous SiO₂@Ag NPs-TB behaved as the label to conjugate with secondary antibody (Ab₂), which also provided another strong detection signals originated from TB confined in such porous structures. The resulting immunosensor displayed a measurable output of procalcitonin (PCT) in the dynamic scope of 0.001 ~ 100 ng mL^-1 with a low limit of detection (LOD) of 0.46 pg mL^-1 (S/N = 3). Moreover, we exploited this strategy for PCT assay in a diluted human serum sample with acceptable results, exhibiting promising applications in the clinical analysis.

Advances in electrochemiluminescence co-reaction accelerator and its analytical applications

Electrochemiluminescence (ECL) can be produced through two main routes: annihilation route and coreactant route. The vast majority of applications of ECL are based on coreactant ECL which can be generated in aqueous media at relatively low potentials compared with organic solvents. However, the development of more efficient ECL systems remains a compelling goal. Co-reaction accelerator (CRA) can significantly enhance the ECL signal through promoting more production of the coreactant intermediate. Compared with other ECL enhancement strategies, the CRA protocol is distinctive owing to its diverse, simple, and highly effective features. Various species such as inorganic compound, organic compound, and nanomaterials (NMs) have been developed as CRA and NM CRA has gained particular attention owing to their unique properties of excellent catalytic behavior and large surface area. By integration with the inherent advantages of ECL, bioanalysis based on CRA-enhanced ECL showed excellent performance such as ultrahigh sensitivity, wide dynamic range, low cost, simple instrumentation, and measurements in complex media. It has been extensively applied in various fields including clinical diagnosis, environmental monitoring, and food safety. Therefore, it is of great interest to present a systematic and critical review on the advances in ECL CRA. Herein, the recent progress on CRA and its applications in ECL bioanalysis are summarized by illustrating some representative work and a discussion of the future development trends of CRA ECL is offered.

Nanosurface energy transfer indicating Exo III-propelled stochastic 3D DNA walkers for HIV DNA detection

DNA-based nanomachines have aroused tremendous interest because of their potential applications in bioimaging, biocomputing, and diagnostic treatment. Herein, we constructed a novel exonuclease III-propelled and signal-amplified stochastic DNA walker that autonomously walked on a spherical particle-based 3D track through a burnt-bridge mechanism, during which nanosurface energy transfer (NSET) occurred between the fluorescent dye modified on hairpin DNA and the surface of gold nanoparticles (AuNPs). As a proof of concept, this stochastic DNA walker achieves prominent detection performance of HIV DNA in the range of 0.05-1.2 nM with a detection limit of 12.7 pM and satisfactory recovery in blood serum, showing high promise in biosensing applications with complicated media.

A label-free electrochemical immunosensor based on encapsulated signal molecules in mesoporous silica-coated gold nanorods for ultrasensitive assay of procalcitonin

For immobilization and signal amplification of the probes, it is feasible and promising by using porous nanomaterials as nanocarriers. Herein, a novel label-free electrochemical immmunosensor was efficiently designed for ultrasensitive detection of procalcitonin (PCT). The immunosensor was prepared by using porous silica-coated gold nanorods (Au NRs@m-SiO₂) to load electroactive dye thionine (Thi) on the electrode surface. Apart from the improved electrical conductivity, the porous feature highly increased the loading amount of Thi to boost the detection signals, while the good biocompatibility and protective microenvironment are beneficial to the largely improved stability for the target. For quantification of PCT, the developed immunosensor exhibited a good linear relationship in the antigen concentration range of 0.001-100 ng mL^-1 with an ultra-low limit of detection (LOD, 0.39 pg mL^-1, S/N = 3). Moreover, the built platform was successfully applied to such assay in human serum samples. The research provides some valuable guidelines for clinical screening and diagnosis of other biomarkers.

An "on-off" electrochemiluminescence immunosensor for PIVKA-II detection based on the dual quenching of CeO2-Au-g-C3N4 hybrids by Ag nanocubes-VB2

Herein, we report a novel dual-quenching electrochemiluminescence (ECL) immunosensor for detecting protein induced by vitamin K absence or antagonist-II (PIVKA-II) based on ECL resonance energy transfer (ECL-RET). In this protocol, self-accelerated ECL hybrids of CeO₂ and Au nanoparticles functionalized g-C₃N₄ nanosheets (CeO₂-Au-g-C₃N₄) were prepared, which exhibited high ECL emission in the presence of S₂O₈^2- as a coreactant for "signal on" state. Concretely, CeO₂ with a reproducible redox couple of Ce³⁺ and Ce⁴⁺ could act as an efficient co-reaction accelerator to generate more oxidizing intermediate (SO₄^•-) to significantly self-promote the ECL emission of g-C₃N₄ NSs/S₂O₈^2- ECL system. Besides, Au nanoparticles not only accelerated electron transfer in the ECL process, but also provided massive active sites for biomolecules immobilization. The dual quenching labels of Ag nanocubes modified with vitamin B₂ (AgNCs-VB₂) were firstly proposed towards g-C₃N₄ NSs/S₂O₈^2- ECL system by ECL-RET, resulting in the remarkable ECL decrease for "signal off" state. Based on the sandwich immunoreaction, the "on-off" PIVKA-II ECL immunosensor gratifyingly possessed excellent detection sensitivity with the linear range of 0.4 pg mL^-1-10 ng mL^-1 and the low detection limit of 28.46 fg mL^-1 (S/N = 3). This presented strategy might provide a potential alternative tool for PIVKA-II detection in medical research and early clinical diagnostics of hepatocellular carcinoma.

Advancement in biosensors for inflammatory biomarkers of SARS-CoV-2 during 2019-2020

COVID-19 pandemic has affected everyone throughout the world and has resulted in the loss of lives of many souls. Due to the restless efforts of the researchers working hard day and night, some success has been gained for the detection of virus. As on date, the traditional polymerized chain reactions (PCR), lateral flow devices (LFID) and enzyme linked immunosorbent assays (ELISA) are being adapted for the detection of this deadly virus. However, a more exciting avenue is the detection of certain biomarkers associated with this viral infection which can be done by simply re-purposing our existing infrastructure. SARS-CoV-2 viral infection triggers various inflammatory, biochemical and hematological biomarkers. Because of the infection route that the virus follows, it causes significant inflammatory response. As a result, various inflammatory markers have been reported to be closely associated with this infection such as C-reactive proteins, interleukin-6, procalcitonin and ferritin. Sensing of these biomarkers can simultaneously help in understanding the illness level of the affected patient. Also, by monitoring these biomarkers, we can predict the viral infections in those patients who have low SARS-CoV-2 RNA and hence are missed by traditional tests. This can give more targets to the researchers and scientists, working in the area of drug development and provide better prognosis. In this review, we propose to highlight the conventional as well as the non-conventional methods for the detection of these inflammatory biomarkers which can act as a single platform of knowledge for the researchers and scientists working for the treatment of COVID-19.

Fe3O4 NP@ZIF-8/MoS2 QD-based electrochemiluminescence with nanosurface energy transfer strategy for point-of-care determination of ATP

Herein, Fe₃O₄ NP@ZIF-8/MoS₂ QD-based electrochemiluminescence (ECL) biosensor with nanosurface energy transfer strategy was successfully developed for point-of-care determination of ATP. With the porous structure and poor electron transfer ability, Fe₃O₄ NP@ZIF-8 complex was first used as an excellent catalyst in ECL. The complex catalyzed the coreactant for more free radicals and hindered the quenching effect of Fe₃O₄ nanoparticles (NPs) on quantum dots (QDs). In ECL-nanosurface energy transfer (NSET) system, through the specific binding of complementary DNA linked to MoS₂ QDs (QDs-cDNA) and aptamer linked to Au NPs, interaction between the point dipole of MoS₂ QDs and the collective dipoles of Au NPs quenched ECL signal. When ATP was captured by aptamer, the ECL-NSET system was taken apart, which resulted in the recovery of ECL signal. Moreover, changes of the ECL imaging can be captured by a smartphone, which enabled point-of-care determination of ATP from 0.05 nmol L^-1 to 200 nmol L^-1 with LOD of 0.015 nmol L^-1. With superior specificity and stability, the sensing system showed significant potential about the application of catalysts coated with ZIF and NSET in point-of-care ECL determination.

Oxygen Vacancy-Enhanced Electrochemiluminescence Sensing Strategy Using Luminol Thermally Encapsulated in Apoferritin as a Transducer for Biomarker Immunoassay

Oxygen vacancies (OVs) enhanced electrochemiluminescence (ECL) biosensing strategy using luminol thermally encapsulated in apoferritin (Lum@apoFt) as an efficient transducer was investigated for ultrasensitive biomarker detection. By applying the oxygen-defect engineering (ODE) strategy, the OVs enriched cobalt-iron oxide (r-CoFe₂O₄) was fabricated as the sensing substrate to boost the electron mobility and catalyze the generation of superoxide anion radical (O₂^•-) for signal amplification. It should be noted that r-CoFe₂O₄ with higher OVs density dramatically accelerated the ECL reaction between O₂^•- and luminol anionic radicals, achieving 6.5-fold stronger ECL output than CoFe₂O₄ with no or low OVs density. Moreover, facile encapsulation of approximate 412 luminol molecules in a single apoFt cavity was first realized by an efficient thermal-induction method. The obtained Lum@apoFt complexes exhibited well-maintained ECL efficiency and excellent biocompatibility for biological modifications. On this basis, a biosensor was developed for early diagnostics of squamous cell carcinomas by detecting its representative biomarker named cytokeratin 19 fragment 21-1 (CYFRA 21-1), from which excellent linearity was achieved in 0.5 pg/mL to 50 ng/mL with a detection limit of 0.14 pg/mL. This work not only put forward a novel idea of creating OVs enriched sensing interface with excellent signal-amplification function but also proposes a facile and robust methodology to design apoFt-based transducers for developing more practical nanoscale biosensors in early diagnostics of diseases.

A wavelength-resolved electrochemiluminescence resonance energy transfer ratiometric immunosensor for detection of cardiac troponin I

In this study, a wavelength-resolved electrochemiluminescence resonance energy transfer (ECL-RET) ratiometric immunosensor from Au nanoparticle functionalized graphite-like carbon nitride nanosheets (Au-g-C3N4) to Au nanoclusters (Au NCs) has been constructed for the first time. At a working voltage of 0 to -1.2 V, Au-g-C3N4 showed a strong cathodic ECL emission with a peak at 460 nm, which overlapped well with the absorption spectra of Au NCs thus stimulating the fluorescence emission of Au NCs at 610 nm. Moreover, within this voltage range, the Au NCs showed no ECL signal; therefore, they would not interfere with the detection of the system. We used cardiac troponin I (cTnI) as an analytical model to construct a sandwich immunosensor based on the ECL-RET ratiometric strategy. By measuring the responses of the ECL460 nm/FL610 nm ratio at different cTnI concentrations, the sensitive detection of cTnI with a wide range of 50 fg mL-1 to 50 ng mL-1 and a low detection limit of 9.73 fg mL-1 can be achieved. This work enriches the wavelength-resolved ECL-RET system and provides an innovative reference for the development of more efficient and sensitive ECL-RET ratiometry.

Washing-free centrifugal microchip fluorescence immunoassay for rapid and point-of-care detection of protein

Simplifying the procedure of immunoassay is still a challenge due to problems such as multiple washing processes, complicated chemical modification and expensive cost. In this study, we developed a portable centrifugal microchip fluorescence immunoassay for washing-free, rapid, quantitative and point-of-care (POC) detection of protein. The designed microchip was fabricated by polycarbonate and assembled by double-sided adhesive tape using injecting molding with high scalability and low cost. The centrifugal strategy is capable of washing-out the bio-fluid and improving signal-to-noise ratio. Matrix nano-spotting method was employed to facilitate satisfactory immunological binding sites with the advantage of high capture efficiency and reproducibility. The proposed approach was capable of sensitively detecting procalcitonin (PCT) with a wide dynamic ranging from 0.10 ng/mL to 70.00 ng/mL within 10 min. Furthermore, this novel integrated diagnostic tool was successfully applied to detect PCT in 101 clinical samples with good consistency with Roche's method, indicating its attractive practical application capability. With favorable simplicity, rapidity, low cost and excellent analytical performance, our method holds great promise for POC diagnostics of proteins.

Hierarchical 0D-2D bio-composite film based on enzyme-loaded polymeric nanoparticles decorating graphene nanosheets as a high-performance bio-sensing platform

Herein, we developed a hierarchical bio-composite sensing film by facile one-step electro-deposition of 0D enzyme-polymer nanoparticles (NPs) with 2D graphene oxide nanosheets as conductive supports and nanofillers, based on which an effective and robust enzymatic biosensor platform was constructed. Horseradish peroxidase (HRP) as a model enzyme was co-assembled with a photo-cross-linkable polypeptide of 2-hydroxyethyl methacrylate modified poly(γ-glutamic acid) (γ-PGA-HEMA), generating hybrid HRP@γ-PGA-HEMA nanoparticles (HRP@PGH NPs). Then HRP@PGH NPs and graphene oxide nanosheets (GO NSs) were simultaneously electrodeposited onto the electrode surface, obtaining a hierarchical 0D-2D bio-composite film. After subsequent electrochemical reduction of GO NSs into graphene nanosheets (GNSs) and following photo-cross-linking, the resultant nanostructured HRP@PGH/GNSs sensing film was successfully applied to construct an enzymatic biosensor for hydrogen peroxide (H₂O₂). The biosensor exerted high sensitivity, fast response, and good stability for H₂O₂ sensing. Satisfactory results were also demonstrated for its practical application in human serum samples, suggesting a promising application potential in biomedical diagnostics. The one-step generated 0D-2D bio-composite sensing film demonstrates synergetic effects from both the soft nanoparticles and hard conductive nanosheets, which would enlighten the innovative construction of composite nanomaterials and nanoarchitectonics for bio-sensing systems.

Triple Amplification of 3,4,9,10-Perylenetetracarboxylic Acid by Co2+-Based Metal-Organic Frameworks and Silver-Cysteine and Its Potential Application for Ultrasensitive Assay of Procalcitonin

In this work, a triple-amplified biosensor with a bioactivity-maintained peculiarity was constructed for quantitative procalcitonin (PCT) detection. As everyone knows, a strong electrochemiluminescence (ECL) signal is the premise to ensure high sensitivity for trace target detection. Hence, a valid tactic was developed to achieve signal amplification of luminophor by using Co²⁺-based metal-organic frameworks (ZIF-67) and silver-cysteine (AgCys). The ZIF-67 particles, which have more atomically dispersed Co²⁺, could play the role of a co-reaction accelerator to catalyze S₂O₈^2- to generate abundant Co³⁺ and sulfate radical anions (SO₄^•-). Afterward, a mass of Co³⁺ was reduced to more hydroxyl radicals (OH^•) by H₂O, thus ulteriorly reducing S₂O₈^2- to generate more SO₄^•-. Remarkably, S₂O₈^2- was reduced to SO₄^•- continuously with the recycling of Co²⁺ and Co³⁺, which realized an effective signal amplification. Meanwhile, the AgCys complex with superior catalysis and biocompatibility was prepared to further improve the ECL signal and maintain the bioactivity of the biomolecule. Furthermore, HWRGWVC, a heptapeptide that was used for combining the Fc fragments of an antibody by Au-S bonding to achieve the fixed point fixation, could not only maintain bioactivity of an antibody but also improved its incubation efficiency, thus further enhancing biosensor sensitivity. Under optimum conditions, the proposed biosensor realized highly sensitive assay for PCT with a wide dynamic range from 10 fg/mL to 100 ng/mL and a detection limit as low as 3.67 fg/mL. With superior stability, selectivity, and repeatability, the prepared biosensor revealed immense potential application of ultrasensitive assay for PCT in human serum.

Sensitive immunosensor based on high effective resonance energy transfer of lucigenin to the cathodic electrochemiluminescence of tris(bipyridine) Ru(II) complex

Electrochemiluminescence resonance energy transfer (ECL-RET) has been attracting much focus as an effective approach for great ECL enhancement. Here, we found that lucigenin (Luc) could serve as a new energy transfer donor and greatly improve the cathodic ECL of bis(2,2'-bipyridyl)(4'-methyl-[2,2']bipyridinyl-4-carboxylicacid) ruthenium(II) (Ru(Bpy)₂(Mcbpy)²⁺, acceptor). Then, both Luc and Ru(Bpy)₂(Mcbpy)²⁺ were largely co-immobilized onto the PdCu nanocrystals and polyethyleneimine (PEI) modified single-walled carbon nanohorns (SWCNHs-PdCuNCs-PEI) through π-π stacking and crosslinking reaction, respectively. By this way, the excellent electrocatalytic behavior and high loading capability for both Luc and Ru(Bpy)₂(Mcbpy)²⁺ of SWCNHs-PdCuNCs-PEI effectively facilitated the ECL reaction. Particularly, the co-immobilization strategy making the donor (Luc)/acceptor (Ru(Bpy)₂(Mcbpy)²⁺) pairs co-exist in the same nano-composite could obviously increase the ECL-RET efficiency by shortening the electron-transfer path and reducing energy loss, further significantly improving the ECL signal. Combining the obtained nano-composite (Luc-SWCNHs-PdCuNCs-PEI-Ru(Bpy)₂(Mcbpy)²⁺) with sandwiched immunoreaction, an ECL immunosensor was constructed for β2-microglobulin (β2-M) measurement. And as a result, it exhibited excellent performance in sensitivity, stability and selectivity. The establishment of the new effective donor/acceptor pairs for ECL-RET and the co-immobilization strategy of making those donor/acceptor pairs largely co-exist in the same nano-composite would greatly improve the ECL efficiency and motivate the wider application of ECL technology.

Novel Electron Donor Encapsulation Assay Based on the Split-type Photoelectrochemical Interface

In this research, a controlled-release photoelectrochemical (PEC) immunosensor is proposed on the basis of a novel encapsulation strategy by all-inorganic semiconductor materials. The controlled-release transmit system has been prepared and represented on account of a group-functional mesoporous silica nanosphere (MSN), utilizing surface-functionalized cadmium sulfide (CdS) nanoparticles as mobilizable caps to encapsulate a PEC electron donor ascorbic acid (AA) within the MSN mesoporous structure. This encapsulation strategy proceeds without any enzyme and acid/alkali to achieve the release of an electron donor. The complex is formed by encapsulating AA within MSN with CdS (CdS@MSN-AA) as a signal amplifier labeled on the secondary antibody. In addition, the immunological recognition process was performed in a 96-well plate, and the reciprocal interference between biorecognition and PEC analysis could be eliminated through a split-type framework. Bi₂S₃-sensitized porous In₂O₃ nanoparticles as a substrate matrix provide basic PEC response. The developed sensor exhibited a mensurable output of procalcitonin (PCT) concentration (as an example) in the detection range of 0.001-200 ng/mL along with a limit of detection of 0.31 pg/mL. Featuring the novel method for electron release, this sensitive PEC strategy provides an innovative way for the potential application for other targets.

Electrogenerated Chemiluminescence Biosensing

This Feature simply introduces the history and mechanism of classical electrogenerated chemiluminescence (ECL) systems for the detection of biomolecules, highlights new advances and emerging fields of the ECL biosensing with recent illustrative examples, and presents the challenges and perspectives of ECL biosensing.

PVP-stabilized tungsten oxide nanoparticles: pH sensitive anti-cancer platform with high cytotoxicity

Photochromic tungsten oxide (WO₃) nanoparticles stabilized by polyvinylpyrrolidone (PVP) were synthesized to evaluate their potential for biomedical applications. PVP-stabilized tungsten oxide nanoparticles demonstrated a highly selective cytotoxic effect on normal and cancer cells in vitro. WO₃ nanoparticles were found to induce substantial cell death in osteosarcoma cells (MNNG/HOS cell line) with a half-maximal inhibitory concentration (IC50) of 5 mg/mL, while producing no, or only minor, toxicity in healthy human mesenchymal stem cells (hMSc). WO₃ nanoparticles induced intracellular oxidative stress, which led to apoptosis type cell death. The selective anti-cancer effects of WO₃ nanoparticles are due to the pH sensitivity of tungsten oxide and its capability of reactive oxygen species (ROS) generation, which is expressed in the modulation of genes involved in reactive oxygen species metabolism, mitochondrial dysfunction, and apoptosis.