Intramolecular Self-Enhanced Nanochains Functionalized by an Electrochemiluminescence Reagent and Its Immunosensing Application for the Detection of Urinary β2-Microglobulin

Confined growth of ultrasmall monodisperse gold nanoparticles in amino functionalized cellulose beads as effective catalysts for 4-nitrophenol reduction

This study aims to prepare a monodisperse catalyst with a space-confined strategy, employing cellulose beads (CBs) as a carrier. Amino functionalized cellulose beads (ACBs) were prepared by grafting polyethyleneimine into the space of CBs via glutaraldehyde cross-linking. The in-situ reduction method was successfully employed to confine monodisperse ultrasmall gold nanoparticles (AuNPs) within the amino functionalized cellulose beads (AuNPs@ACBs) matrix. The AuCl4- ions were first immobilized on the amino substance (such as -NH3+/-NH2+, CN and CN) by chelation and electrostatic interaction. Then the Au(III) was reduced to Au(0) by electron transfer. The presence of amino groups in ACBs controls the size and dispersion of AuNPs. AuNPs@ACBs was used as a catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), it reveals excellent catalytic activity, which can be ascribed to the smaller particle size of AuNPs (TOF = 7.86 min-1). The spherical structure of AuNPs@ACBs permits straightforward recovery from the aqueous solution after the reaction is completed, thus improving the reusability and catalytic stability. The catalytic efficiency of AuNPs@ACBs can still reach 64.7 % after 10 cycles. After more than 3000 min, the column continues to run without detecting 4-NP in the eluent, which is still working.

Nano-matrixes propped self-enhanced electrochemiluminescence biosensor for microRNA detection

MicroRNAs (miRNA) are the potential biomarker for breast cancer, a biosensor for detecting miRNA-21 was successfully prepared by covalently linking carbohydrazide (CON4H6) and tris (4,4 '- dicarboxylic acid-2,2' - bipyridyl) ruthenium dichloride (Ru (dcbpy)32+) as a self-enhanced emitter (Ru-CON4H6). The biosensor was prepared by coating the electrode with mesoporous silica encapsulated Ru-CON4H6 as luminophores (RMSNs) to covalently link a couple of DNA strands (Q1-H2). The RMSNs coated electrode exhibited strong ECL emission due to the intramolecular electron transfer between the electrochemically oxidized Ru (dcbpy)32+ and co-reactant CON4H6. In the presence of target miRNA-21 and an assistant hairpin H1, H2 could be released from the surface through a strand displacement reaction (SDR), and the reserved Q1 could form G-quadruplex upon the addition of K+. The formed G-quadruplex then interacted with Q2-Fc in the presence of Mg2+ to form a DNA complex on the biosensor surface, which quenched the nano-matrixes propped self-enhanced ECL emission through the electron exchange between Fc and electrode or oxidized ECL intermediates. Under optimal conditions, the ECL decrease showed a correlation with target concentration, leading to a biosensing method for sensitive detection of miRNA-21. The proposed ECL method demonstrated a detectable concentration range from 0.1 fM to 1 nM along with a detection limit of 0.03 fM, good accuracy, and acceptable reproducibility, showing that the self-enhanced ECL biosensing strategy supported by nano-matrix provided a new way for the ultrasensitive detection of miRNA, and promoted the development of breast cancer diagnosis.

A self-enhanced electrochemiluminescence array chip for portable label-free detection of SARS-CoV-2 nucleocapsid protein with smartphone

SARS-CoV-2 antigen detection plays a key role in the rapid diagnosis of COVID-19. However, current clinically used immunoassays are often limited by assay throughput, sensitivity, accuracy, and field operating conditions. To address these challenges, we constructed a self-enhanced electrochemiluminescence (ECL) array chip (SE2AC) for highly sensitive and label-free detection of SARS-CoV-2 nucleocapsid protein (N protein) with a facile and portable assay setup. Firstly, the self-enhanced ECL nanomaterials with inherent film-forming properties were synthesized by co-doping Ru(bpy)32+ and polyethyleneimine (PEI) in silica nanoparticles (Ru/PEI@SiO2). Secondly, a resistance-induced potential difference-based single-electrode electrochemical system (SEES) was adapted to serve as the electrode array to facilitate one-step assembly without the need for chip alignment. Thirdly, the chip electrode array was functionalized with the synthesized self-enhanced ECL emitters and captured antibodies. In addition, a portable detection box equipped with a smartphone was 3D-printed to serve as the chip holder and "dark room" for imaging acquisition. The SE2AC performance was validated with N protein with a limit of detection (LOD) of 0.47 pg/mL in the range of 1-10,000 pg/mL. Furthermore, the chip successfully detected the viral antigen residue as low as 1.92 pg/mL from diluted rehabilitation patients' serum samples. This is the first study reporting label-free detection of SARS-Cov-2 N protein based on a self-enhanced ECL immunosensor, which provides a novel facile method for highly sensitive diagnosis of COVID-19 with high throughput, portability, and low cost.

A novel efficient intramolecular self-enhanced water-soluble iridium-based electrochemiluminescence reagent and its analytical application in aptamer sensor

In order to overcome the poor solubilities of iridium-based ECL luminophores and explore self-enhanced ECL luminophores, polyethyleneimine (PEI) covalently linked with iridium complex via amide bonds (abbreviated as Ir-PEI) as a new novel intramolecular self-enhanced water-soluble ECL reagent has been unprecedently designed and successfully synthesized in this work. The chemical structure data, FT-IR spectra, photophysical, electrochemical and electrochemiluminescence of this new ECL reagent have been well characterized. In addition, in order to investigate its properties in the real applications, a corresponding new sensitive and specific ECL-based aptasensor to monitor tetracycline (TET) residues in honey and lake water has been further constructed based on this novel self-enhanced reagent of Ir-PEI in this work. This as-prepared intramolecular self-enhanced water-soluble of Ir-PEI illustrated in this work would pave a new avenue to promote the analytical applications of iridium-based ECL luminophores in the future.

Dual-potential electrochemiluminescence cytosensor based on a metal-organic framework and ABEI-PEI-Au@AgNPs for the simultaneous determination of phosphatidylserine and epidermal growth factor receptors on an apoptotic cell surface

A new electrochemiluminescence (ECL) cytosensor is proposed for the simultaneous determination of phosphatidylserine (PS) and epidermal growth factor receptor (EGFR) based on the ECL signals of metal-organic framework-5 (MOF-5) loaded CdS quantum dots and N-(aminobutyl)-N-(ethylisoluminol)-polyethylenimine capped Au and Ag nanoparticles. Apoptosis promotes the exposure of PS and reduces the expression of EGFR in cell membranes. Two spatially resolved areas on dual-disk glassy carbon electrodes were designed to eliminate the interference from different ECL probes. Using HepG2 cells treated with resveratrol to induce apoptosis, the cytosensor exhibited high sensitivity, simplicity, and high reproducibility, demonstrating its potential in drug screening and rapid apoptotic cell detection. The strategy reported provides a promising platform for the highly sensitive cytosensing and convenient screening of clinically relevant anticancer drugs.

Identification of early stage and metastatic prostate cancer using electrochemical detection of beta-2-microglobulin in urine samples from patients

To improve prostate cancer (PCa) diagnosis, it is imperative to identify novel biomarkers and establish effective screening techniques. Here, we introduce electrochemical biosensing of β-2-Microglobulin (β2M) in urine as a potential diagnostic tool for PCa. The immunosensor is composed of a screen-printed graphene electrode coated with anti β2M antibodies. The sensor is capable of detecting the protein directly in urine without any sample pretreatment within 45 min including sample incubation and a lower limit of detection of 204 µg/L. The sensor demonstrated a significant difference in the β2M-creatinine ratio in urine between control and both local- and metastatic PCa (mPCa) (P = 0.0302 and P = 0.0078 respectively), and between local- and mPCa (P = 0.0302). This first example of electrochemical sensing of β2M for the diagnosis of PCa may set the stage for an affordable, on-site screening technique for PCa.

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.

A signal "on-off-on"-type electrochemiluminescence aptamer sensor for detection of sulfadimethoxine based on Ru@Zn-oxalate MOF composites

An "on-off-on"-type electrochemiluminescence (ECL) aptamer sensor based on Ru@Zn-oxalate metal-organic framework (MOF) composites is constructed for sensitive detection of sulfadimethoxine (SDM). The prepared Ru@Zn-oxalate MOF composites with the three-dimensional structure provide good ECL performance for the "signal-on." The MOF structure with a large surface area enables the material to fix more Ru(bpy)₃²⁺. Moreover, the Zn-oxalate MOF with three-dimensional chromophore connectivity provides a medium which can accelerate excited-state energy transfer migration among Ru(bpy)₃²⁺ units, and greatly reduces the influence of solvent on chromophore, achieving a high-energy Ru emission efficiency. The aptamer chain modified with ferrocene at the end can hybridize with the capture chain DNA1 fixed on the surface of the modified electrode through base complementary pairing, which can significantly quench the ECL signal of Ru@Zn-oxalate MOF. SDM specifically binds to its aptamer to separate ferrocene from the electrode surface, resulting in a "signal-on" ECL signal. The use of the aptamer chain further improves the selectivity of the sensor. Thus, high-sensitivity detection of SDM specificity is realized through the specific affinity between SDM and its aptamer. This proposed ECL aptamer sensor has good analytical performance for SDM with low detection limit (27.3 fM) and wide detection range (100 fM-500 nM). The sensor also shows excellent stability, selectivity, and reproducibility, which proved its analytical performance. The relative standard deviation (RSD) of SDM detected by the sensor is between 2.39 and 5.32%, and the recovery is in the range 97.23 to 107.5%. The sensor shows satisfactory results in the analysis of actual seawater samples, which is expected to play a role in the exploration of marine environmental pollution.

Au (III) cross-linked hollow organosilica capsules from 3-aminopropyltriethoxysilane

Hollow organosilica capsules have received extensive interest due to their application potentials in catalyst, sensor, drug delivery etc. In this work, we demonstrate a novel strategy to fabricate hollow organosilica capsules based on coordination interaction, by using 3-aminopropyltriethoxysilane (APTES) as precursor and Au (III) as cross-linker. In this approach, stable APTES droplets are first formed in water with the presence of Au (III) due to the coordination effect between Au (III) and the amino groups of APTES located on the surface of the droplets. Subsequently, the self-catalyzed hydrolysis/condensation of APTES allows for the formation of hollow organosilica capsules, in which the droplets of APTES themselves act as soft template and the Au (III) as cross-linker. The formation mechanism of the capsules was investigated, and potential of the as-prepared Au (III) cross-linked hollow organosilica capsules as glutathione (GSH) sensitive drug carriers was evaluated. In addition, Au particle embedded hollow capsules are further obtained by in-situ reduction of the Au (III) in the shell, which showed excellent stability towards the cyclic catalytic reductions of p-nitroaniline.

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.

Fabrication of a ratiometric electrochemiluminescence biosensor using single self-enhanced nanoluminophores for the detection of spermine

A ratiometric electrochemiluminescence strategy using a single luminophore for accurate and sensitive biomolecule detection could be immensely valuable in bioanalysis. Herein, an ultrasensitive ratiometric electrochemiluminescence sensing system was fabricated using a self-enhanced luminophore with dual-signal emission for the detection of spermine. A nanocomposite was synthesized by the covalent attachment of N, N-diisopropylethylenediamine onto glutathione-protected Au-Ag bimetallic nanoclusters (DPEA-GSH@Au/Ag BNCs). The nanocomposite exhibited efficient intra-cluster charge transfer to produce strong anodic self-enhanced electrochemiluminescence emission at 0.8 V without external co-reactants. Interestingly, the DPEA@GSH@Au-Ag BNCs exhibited cathodic electrochemiluminescence emission upon the addition of the co-reactant potassium persulfate at -1.6 V, exhibiting stable and efficient dual-signal electrochemiluminescence emission features at a continuous potential window of -1.75 to 1.2 V. Thus, they were used to fabricate a single-luminophore electrochemiluminescence sensor with dual emission. The cathodic emission of the biosensor gradually increased with increasing concentrations of spermine, whereas the anodic electrochemiluminescence intensity remained almost constant, enabling the ratiometric detection of spermine. The fabricated biosensor, with an internal standard, significantly improved the accuracy and reliability of spermine detection in a wide concentration range of 0.85 pM-100 μM, with a low limit of detection of 0.12 pM (S/N = 3) under optimum conditions. This single-luminophore electrochemiluminescence sensing system could be used for the detection of spermine and could guide the construction of ratiometric electrochemiluminescence sensors in the future.

Lifting the Veil: Characteristics, Clinical Significance, and Application of β-2-Microglobulin as Biomarkers and Its Detection with Biosensors

Because β-2-microglobulin (β₂M) is a surface protein that is present on most nucleated cells, it plays a key role in the human immune system and the kidney glomeruli to regulate homeostasis. The primary clinical significance of β₂M is in dialysis-related amyloidosis, a complication of end-stage renal disease caused by a gradual accumulation of β₂M in the blood. Therefore, the function of β₂M in kidney-related diseases has been extensively studied to evaluate its glomerular and tubular functions. Because increased β₂M shedding due to rapid cell turnover may indicate other underlying medical conditions, the possibility to use β₂M as a versatile biomarker rose in prominence across multiple disciplines for various applications. Therefore, this work has reviewed the recent use of β₂M to detect various diseases and its progress as a biomarker. While the use of state-of-the-art β₂M detection requires sophisticated tools, high maintenance, and labor cost, this work also has reported the use of biosensor to quantify β₂M over the past decade. It is hoped that a portable and highly efficient β₂M biosensor device will soon be incorporated in point-of-care testing to provide safe, rapid, and reliable test results.

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.

Highly sensitive competitive electrochemiluminescence immunosensor based on ABEI-H2O2 system with cobalt hydroxide nanosheets and bimetal PdAg as co-enhancer for detection of florfenicol

A competitive electrochemiluminescence immunoassay was established based on the isoluminol-H₂O₂ (ABEI-H₂O₂) system catalyzed by cobalt hydroxide (Co(OH)₂) to detect florfenicol residues in food. First , ultra-thin two-dimensional Co(OH)₂ nanosheets were used as the catalyst of ABEI-H₂O₂ system, and excellent catalytic effects were acquired by catalytic decomposition of hydrogen peroxide with cobalt ions. Then, bimetal PdAg (Pd/Ag) alloy nanoparticles were used as a bridge to connect ABEI and antibody due to their good biocompatibility; Pd/Ag alloy nanoparticles also had a catalytic effect to further amplify the ECL signal in the system due to the synergistic catalytic effect of the bimetal. A competitive immunoassay strategy was used to detect florfenicol, where the florfenicol in the sample will compete with the antibody for the limited binding sites on the coating antigen. The ECL immunosensor for florfenicol detection shows high sensitivity, with a linear range from 10^-4  to 10² ng mL^-1, and a detection limit of 3.1 × 10^-5 ng mL^-1, where the scan potential was varied from 0 to 0.6 V vs Ag/AgCl . This work was the first to use Co(OH)₂ nanosheets and bimetal PdAg catalytic signal amplification methods to design the sensor, which provides a novel, convenient and reliable strategy for ultra-sensitive detection of florfenicol, and other biological small molecules. A novel ECL immunosensor based on ABEI-H₂O₂₂.

Colorimetric detection of human alpha-2-macroglobulin by janus imprinted nanoparticles constructed dual molecular imprinting immunosandwich strategy

Simple and rapid detection of disease-related bio-markers are significant for early clinical diagnosis and can potentially improve the survival rate. However, establishing a high-specificity colorimetric detection method for bio-markers are still challenges due to their inevitable natural antibody used or enzymatic labeling. Herein, a cost-efficient and easy-to-use approach, which called dual molecular imprinting immunosandwich colorimetric strategy (DMI-ICS) was constructed for detection alpha-2-macroglobulin (α2MG) by janus imprinted nanoparticles. The unique detection principle was contained with two mimic antibody parts, the first part was α2MG glass slides molecularly imprinted material (GS-MIP) as a "Separation antibody", which can specifically rapid separate the protein in the complex sample; Another part was asymmetrically modified janus molecularly imprinted gold nanoparticles nanozyme (J-GNPs-MIP) as a "Detection antibody", which has the properties of specific recognition and catalytic substrate color performance at the same time. The concentration of α2MG can be determined by the substrate color changes and observed with naked eyes. Under the optimized conditions, the DMI-ICS had a great performance and offering lower relative standard deviation (RSD, 7.69%), good linear range (0.297-130 μg/mL, R² = 0.994), high imprinting factor (IF: 3.74) with lower detection limit (0.089 μg/mL). This strategy provides an easy operation and low cost signal readout method for direct detection and separation of α2MG in human serum samples, which is a versatile tool for point-of-care diagnosis, while also offering a new perspective on antibody simulation technology, multifunctional antibody preparation and contribute to detection of disease-related bio-marker in nonspecialized laboratory infrastructure.

Electrochemiluminescence biosensor for microRNA determination based on AgNCs@MoS2 composite with (AuNPs-Semicarbazide)@Cu-MOF as coreaction accelerator

A novel electrochemiluminescence (ECL) biosensor was fabricated for miRNA-162a detection by using silver nanoclusters/molybdenum disulfide (AgNCs@MoS₂) as an ECL material, peroxodisulfate (S₂O₈^2-) as a co-reactant, and semicarbazide (Sem) as a co-reaction accelerator. Firstly, hairpin probe H_a modified on AgNCs@MoS₂/GCE was unfolded based on its hybridization with target microRNA. Then, the unfolded H_a can further be hybridized with another hairpin DNA of H_b on (AuNPs-semicarbazide)@Cu-MOF, resulting in the release of target microRNA, which further causes a cyclic hybridization. This creates more (AuNPs-semicarbazide)@Cu-MOF on the electrode surface, achieving cyclic hybridization signal amplification. Strikingly, due to the presence of Sem, accelerating the reduction of S₂O₈^2- and resulting in the generation of more oxidant intermediates of SO₄^2-, the amount of excited states of Agincreases to further amplify the ECL signal. The biosensor exhibited high sensitivity with a low LOD of 1.067 fM, indicating that the introduction of co-reaction accelerators can provide an effective method for signal amplification. The applicability of this method was assessed by investigating the effect of Pb(II) ion on miRNA-162a expression level in maize seedling leaves. A novel electrochemiluminescence biosensor was fabricated for miRNA-162a detection by using silver nanoclusters/molybdenum disulfide as an ECL material, peroxodisulfate as a co-reactant, and semicarbazide as a co-reaction accelerator.

A highly sensitive electrochemiluminescence immunosensor for h-FABP determination based on self-enhanced luminophore coupled with ultrathin 2D nickel metal-organic framework nanosheets

In this work, a novel ECL immunosensor based on self-enhanced luminophore and ultrathin 2D nickel MOF nanosheets was fabricated for sensitive and specific detection of h-FABP. Initially, the porous ultrathin Ni-TCPP (Fe) nanosheets with high specific surface area and plentiful active sites were newly synthesized, which could enhance ECL signal of luminol by the superior peroxidase mimics activity towards H₂O₂ decomposition. Then, PEI and luminol were simultaneously immobilized on Ni-TCPP (Fe) nanosheets to construct self-enhanced solid state luminophore (Ni-TCPP (Fe)-PEI-Lum), possessing desirable stability and high ECL efficiency. Furthermore, poly (indole-5-carboxylic acid) (PICA) worked as substrate with outstanding conductivity and abundant binding sites to improve sensitivity. Under optimal conditions, the designed ECL immunosensor exhibited a wide dynamic range from 100 fg mL^-1 to 100 ng mL^-1 and a low detection limit of 44.5 fg mL^-1. In addition, the ECL immunosensor behaved excellent specificity and was successfully applied to detect target h-FABP protein in complex physiological matrix. Therefore, this work may provide an alternative method for biomarker detection in clinical diagnosis and expand the application potential of 2D MOF nanosheets in ECL technique.

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.

Electrochemiluminescence detection of cardiac troponin I based on Au–Ag alloy nanourchins

In this work, an Au–Ag alloy nanourchin (Au–Ag alloy NU) based electrochemiluminescent (ECL) sensor for the measurement of cardiac troponin I (cTnI) was developed.

ATMP-induced three-dimensional conductive polymer hydrogel scaffold for a novel enhanced solid-state electrochemiluminescence biosensor

Reliable and sensitive detection of xanthine has important medical and biological significance. In this work, a novel three-dimensional (3D) conductive polymer hydrogel of polyaniline (PAni) was feasibly prepared using aniline (Ani), amino trimethylene phosphonic acid (ATMP) and ammonium persulfate ((NH₄)₂S₂O₈) as monomer, gelatinizing agent and oxidizing agent, respectively. Protonation of aniline can be achieved by ATMP, inducing good conductivity of the obtained hydrogel. ATMP remained the chelating abilities in the conductive hydrogel, enabling further immobilization with silver nanoparticles (AgNPs) functionalized by a luminol derivative, N-(aminobutyl)-N-(ethylisoluminol) (ABEI). ABEI-Ag@PAni-ATMP exhibited an enhanced performance of solid-state electrochemiluminescence (ECL). Integrated with xanthine oxidase (XOD), the proposed biosensor can be applied in the detection of xanthine via in-situ generated hydrogen peroxide (H₂O₂), and present a low detection limit of 9.6 nM, a wide linear range (from 0.01 to 200 μM) and excellent stability.

Highly sensitive bioaffinity electrochemiluminescence sensors: Recent advances and future directions

Electrogenerated chemiluminescence (also called electrochemiluminescence and abbreviated ECL) has attracted much attention in various fields of analysis due to the potential remarkably high sensitivity, extremely wide dynamic range and excellent controllability. Electrochemiluminescence biosensor, by taking the advantage of the selectivity of the biological recognition elements and the high sensitivity of ECL technique was applied as a powerful analytical device for ultrasensitive detection of biomolecule. In this review, we summarize the latest sensing applications of ECL bioanalysis in the field of bio affinity ECL sensors including aptasensors, immunoassays and DNA analysis, cytosensor, molecularly imprinted sensors, ECL resonance energy transfer and ratiometric biosensors and give future perspectives for new developments in ECL analytical technology. Furthermore, the results herein discussed would demonstrate that the use of nanomaterials with unique chemical and physical properties in the ECL biosensing systems is one of the most interesting research lines for the development of ultrasensitive electrochemiluminescence biosensors. In addition, ECL based sensing assays for clinical samples analysis and medical diagnostics and developing of immunosensors, aptasensors and cytosensor for this purpose is also highlighted.

Dual-Signaling Amplification Electrochemical Aptasensor Based on Hollow Polymeric Nanospheres for Acetamiprid Detection

In this work, we first reported a dual-signaling electrochemical aptasensor based on layer-by-layer template technology and catalytic amplification for acetamiprid detection. Herein, the signal probe of the ferrocene (Fc)-based hollow polymeric nanospheres (Fc-HPNs) were prepared with repeated electrostatic adsorption between anionic poly(acrylic acid) and hyperbranched cationic polyethylenimine. In addition, ascorbic acid (AA) as an enhancer can catalyze the reduction of Fc-HPNs, which results in significant enhancement of the oxidation peak current of Fc-HPNs. Remarkably, the Fc-HPNs played dual roles: as nanocarriers to significantly increase the load amount of Fc and as nanoreducers to effectively catalyze reduction by AA for further signal amplification. Therefore, because of the special nanostructures of Fc-HPNs and the effective catalytic effect of AA, a dual-signaling electrochemical aptasensor was proposed. Surprisingly, this proposed assay for trace amounts of target detection exhibits excellent sensitivity with a linear range from 10 nM to 1 fM and a limit of detection down to 0.33 fM (S/N = 3), which opened a novel avenue and versatile strategy for monitoring of acetamiprid.

Enzyme-free Target Recycling and Double-Output Amplification System for Electrochemiluminescent Assay of Mucin 1 with MoS2 Nanoflowers as Co-reaction Accelerator

In this work, a sensitive electrochemiluminescent assay of mucin 1 (MUC1) was developed with the advantages of target recycling amplification strategy and effective MoS₂ nanoflower (MoS₂ NF)-based signal probe. Briefly, the target MUC1 triggered enzyme-free recycling and a double-output amplification process was executed to acquire masses of single-stranded DNA as a mimic target, which further participated in the catalytic hairpin assembly process for signal amplification. Meanwhile, MoS₂ NFs were prepared as an effective co-reaction accelerator, which not only possessed excellent catalytic performance for H₂O₂ decomposition to largely enhance the luminous intensity of N-(aminobutyl)- N-(ethylisoluminol) (ABEI)-H₂O₂ electrochemiluminescence system but also offered a desirable platform for ABEI-functionalized Ag nanoparticles (ABEI-Ag complexes) loading via Ag-S binding. The experimental results showed the proposed aptasensor had a good linear relationship in the range of 1 fg/mL to 10 ng/mL for MUC1 detection and the limit of detection was 0.58 fg/mL (S/N = 3). In addition, the aptasensor had nice stability and selectivity and huge potential to be applied in clinical research.