Ternary BiOI/Bi2S3/Au Nanosheet Arrays as a Photoelectrochemical Signal Converter for the Detection of Cardiac Troponin I.

Nanosheet arrays with stable signal output have become promising photoactive materials for photoelectrochemical (PEC) immunosensors. However, an essential concern is the facile recombination of carriers in one-component nanoarrays, which cannot be readily prevented, ultimately resulting in weak photocurrent signals. In this study, an immunosensor using gold nanoparticle-anchored BiOI/Bi2S3 nanosheet arrays (BiOI/Bi2S3/Au) as a signal converter was fabricated for sensitive detection of cardiac troponin I (cTnI). The ternary nanosheet arrays were prepared by a simple method in which Bi2S3 was well-coated on the BiOI surface by in situ growth, whereas the addition of Au further improved the photoelectric conversion efficiency and could link more antibodies. The three-dimensional (3D) ordered sheet-like network array structure and BiOI/Bi2S3/Au ternary nanosheet arrays showed stable and high photoelectric signal output and no significant difference in signals across different batches under visible light excitation. The fabricated immunosensor has a sensitive response to the target detection marker cTnI in a wide linear range of 500 fg/mL to 50 ng/mL, and the detection limit was 32 fg/mL, demonstrating good stability and selectivity. This work not only shows the great application potential of ternary heterojunction arrays in the field of PEC immunosensors but also provides a useful exploration for improving the stability of immunosensors.

MIBPred: Ensemble Learning-Based Metal Ion-Binding Protein Classifier.

In biological organisms, metal ion-binding proteins participate in numerous metabolic activities and are closely associated with various diseases. To accurately predict whether a protein binds to metal ions and the type of metal ion-binding protein, this study proposed a classifier named MIBPred. The classifier incorporated advanced Word2Vec technology from the field of natural language processing to extract semantic features of the protein sequence language and combined them with position-specific score matrix (PSSM) features. Furthermore, an ensemble learning model was employed for the metal ion-binding protein classification task. In the model, we independently trained XGBoost, LightGBM, and CatBoost algorithms and integrated the output results through an SVM voting mechanism. This innovative combination has led to a significant breakthrough in the predictive performance of our model. As a result, we achieved accuracies of 95.13% and 85.19%, respectively, in predicting metal ion-binding proteins and their types. Our research not only confirms the effectiveness of Word2Vec technology in extracting semantic information from protein sequences but also highlights the outstanding performance of the MIBPred classifier in the problem of metal ion-binding protein types. This study provides a reliable tool and method for the in-depth exploration of the structure and function of metal ion-binding proteins.

A ZnIn2S4/Ag2CO3 Z-scheme heterostructure-based photoelectrochemical biosensor for neuron-specific enolase.

An efficient photo-to-electrical signal is pivotal to photoelectrochemical (PEC) biosensors. In our work, a novel PEC biosensor was fabricated for the detection of neuron-specific enolase (NSE) based on a ZnIn2S4/Ag2CO3 Z-scheme heterostructure. Due to the overlapping band potentials of the ZnIn2S4 and Ag2CO3, the formed Z-scheme heterostructure can promote the charge separation and photoelectric conversion efficiency. And the concomitant Ag nanoparticles in Ag2CO3 provided multiple functions to enhance the PEC response of the Z-scheme heterostructure. It acts not only as a bridge for the transfer of carriers between ZnIn2S4 and Ag2CO3, promoting the constructed Z-scheme heterostructure, but also as electron mediators to accelerate the transfer of photogenerated carriers and improve the capture of visible light of the Z-scheme heterostructure by surface plasmon resonance (SPR). Compared with single Ag2CO3 and ZnIn2S4, the photocurrent of the designed Z-scheme heterostructure increased more than 20 and 60 times respectively. The fabricated PEC biosensor based on a ZnIn2S4/Ag2CO3 Z-scheme heterostructure exhibits sensitive detection to NSE, and presents a linear range of 50 fg·mL-1 ~ 200 ng·mL-1 with a limit of detection of 4.86 fg·mL-1. The proposed PEC biosensor provides a potential approach for clinical diagnosis.

Sandwich-type electrochemical immunosensor based on CuFe2O4-Pd for cardiac troponin I detection.

A sandwich-type electrochemical immunosensor was designed by highly efficient catalytic cycle amplification strategy of CuFe2O4-Pd for sensitive detection of cardiac troponin I. CuFe2O4 with coupled variable valence metal elements exhibited favorable catalytic performance through bidirectional cycling of Fe2+/Fe3+ and Cu+/Cu2+ redox pairs. More importantly, Cu+ acted as the intermediate product of the catalytic reaction, promoted the regeneration of Fe2+ and ensured the continuous recycling occurrence of the double redox pairs, and significantly amplified the current signal response. Pd nanoparticles (Pd NPs) loaded on the surface of amino-functionalized CuFe2O4 (CuFe2O4-NH2) served as electrochemical mediators to capture labeled antibodies (Ab2), and also as co-catalysts of CuFe2O4 to further enhance the catalytic efficiency, thus improving the sensitivity of the electrochemical immunosensor. Under the optimal experimental conditions, the linear range was 0.001 ~ 100 ng/mL, and the detection limit was 1.91 fg/mL. The electrochemical immunosensor has excellent analytical performance, giving a new impetus for the sensitive detection of cTnI.

Integrating reduced amino acid composition into PSSM for improving copper ion-binding protein prediction.

Copper ion-binding proteins play an essential role in metabolic processes and are critical factors in many diseases, such as breast cancer, lung cancer, and Menkes disease. Many algorithms have been developed for predicting metal ion classification and binding sites, but none have been applied to copper ion-binding proteins. In this study, we developed a copper ion-bound protein classifier, RPCIBP, which integrating the reduced amino acid composition into position-specific scoring matrix (PSSM). The reduced amino acid composition filters out a large number of useless evolutionary features, improving the operational efficiency and predictive ability of the model (feature dimension from 2900 to 200, ACC from 83 % to 85.1 %). Compared with the basic model using only three sequence feature extraction methods (ACC in training set between 73.8 %-86.2 %, ACC in test set between 69.3 %-87.5 %), the model integrating the evolutionary features of the reduced amino acid composition showed higher accuracy and robustness (ACC in training set between 83.1 %-90.8 %, ACC in test set between 79.1 %-91.9 %). Best copper ion-binding protein classifiers filtered by feature selection progress were deployed in a user-friendly web server (http://bioinfor.imu.edu.cn/RPCIBP). RPCIBP can accurately predict copper ion-binding proteins, which is convenient for further structural and functional studies, and conducive to mechanism exploration and target drug development.

Mixed-Ligand-Regulated Self-Enhanced Luminous Eu-MOF as an ECL Signal Probe for an Oriented Antibody-Decorated Biosensing Platform.

The self-luminescence behavior of lanthanide MOFs (Ln-MOFs) due to the unique antenna effect is considered to be a promising electrochemiluminescence (ECL) emission for biosensors. It is more challenging for Ln-MOFs on account of the difficulty to stimulate Ln ions with the desired energy-transfer efficiency to produce stronger ECL emissions at a low potential. Here, guided by a second ligand-assisted energy-transfer strategy, we present an efficient self-enhanced luminescence mixed-ligand Eu-MOF as an ECL signal probe for an oriented antibody-decorated biosensing platform with a low detection limit and a broad detection range. Diamino terephthalic acid (NH2-H2BDC) and 1,10-phenanthroline (Phen) were selected as the first and second ligands, respectively, to form highly conjugated structures, as well as suppress the nonradiative energy transfer. Impressively, Phen precisely adjusts the energy gap between the triplet ligand and the excited state of Eu3+, realizing the self-enhancement of ECL efficiency of the Eu-MOF. The mixed ligand adjusted the molar ratio to obtain the stable and strong ECL signal at a lowered triggering potential (0.83 V). In addition, FeCo@CNT features densely active FeCo sites along with a rich hierarchy conductive carbon nanotube (CNT) network, which is efficiently a co-reaction accelerator to produce more TPA•+ radicals to accelerate the reduction process of the Eu-MOF for achieving the ECL emission amplification. FeCo@CNT with heptapeptide HWRGWVC (HWR) constructed a matrix biosensing interface that allowed the fragment antigen-binding (Fab) regions to target specific antigens and enhance the incubation efficiency. The present study has gone some way toward designing a self-enhanced luminous Eu-MOF, thus giving new fresh impetus to develop high-performance ECL emitters for biological analysis.

Sandwich-type electrochemical immunosensor based on nitrogen-doped porous carbon and nanoporous trimetallic nanozyme (PdAgCu) for determination of prostate specific antigen.

A sandwich-type electrochemical immunosensor was designed for the ultrasensitive detection of prostate-specific antigen (PSA), using Au nanoparticles (Au NPs) modified nitrogen-doped porous carbon (NPC) as sensor platform and trimetallic PdAgCu mesoporous nanospheres (PdAgCu MNSs) as enzyme-mimicking labels. NPC was prepared by a facile one-step pyrolysis strategy of biomimetic phylloid zeolite imidazole framework (ZIF-L) nanosheets. Through this strategy, the graphitization of the microcrystalline structure enhanced the electrical conductivity, while its enlarged specific surface area and abundant pore volume can enrich H2O2 to improve the catalytic efficiency. Moreover, Au NPs were used to modify NPC without cross-linking agents to further optimize electron transport while capturing primary antibodies, improving stability and sensitivity of the immunosensor. PdAgCu MNSs with uniform size, cylindrical open mesoporous channels, and continuous crystal frame structure were self-assembling synthesized by electrostatic adsorption and ascorbic acid (AA) co-reduction with amphiphilic dioctadecyldimethylammonium chloride (DODAC) as surfactant-cum-micelle, whose unique structure maximizes the use of polyatoms to expose catalytic sites, exhibiting good biocompatibility and electrocatalytic ability. Under the optimal conditions, the immunosensor showed superior sensitivity, a wide dynamic detection range (10 fg mL-1 ~ 100 ng mL-1) and a low limit of detection (LOD, 3.29 fg mL-1). This work provides a convenient strategy for the clinical detection of PSA.

Ultrasensitive photoelectrochemical immunosensor based on Dual-Photosensitive electrodes.

In the study, a photoelectrochemical (PEC) immunosensor based on dual-photosensitive electrodes was developed for cardiac troponin I (cTnI) detection. The sensing photocathode with biometric functions was prepared by CuInS2 and narrow band gap semiconductor In2S3 as the counter electrode. In this way, the separation of photoanode and biometric events was realized, and the ability of stability of the immunosensor could be effectively improved. Moreover, the attraction to the photogenerated electrons (e-) from photoanode would be increased by the abundant holes (h+) of photocathode, under the radiation of light. This tremendously improves the photoelectric response, which further improves the sensitivity of the immunosensor. The controllable-synthesis uncomplicated photoelectric material not only accords with the principle of simplicity of electrode modification but also makes the immunosensor more conducive to the practical application. Additionally, even in the case of zero bias voltage, the constructed PEC immunosensor can operate with high efficiency, namely, self-powered. The immunosensor could provide the quantitative readout photocurrent to a concentration of cTnI in the range of 0.10 pg/mL to 1.00 µg/mL and the detection limit was 0.0113 pg/mL under the optimal experimental conditions. With favorable performance in terms of anti-interference, stability, specificity and reproducibility, this immunosensor will provide new prospects for general PEC bioanalysis development.

A "signal-off" electrochemiluminescence biosensing platform based on high efficiency quenching effect of functionalized copper oxide toward glutathione-gold nanoclusters.

A "signal-off" Electrochemiluminescence (ECL) biosensing platform based on Glutathione-Au nanoclusters covered reduced graphene oxide (GSH-Au NCs@rGO) and Au nanoparticles functionalized copper oxide (Au@CuO) was fabricated. The GSH ligand protected Au NCs were spontaneously adsorbed on the rGO surface via Van der Waals force. As ECL emitters, GSH-Au NCs@rGO not only support more luminophores and immobilization of bioreceptor units also facilitates mass transfer, accelerating ECL excitation to obtain a higher ECL signal intensity. Remarkably, Au@CuO with good biocompatibility was first applied as a quenching probe. Au@CuO (acceptor)-dependent resonance energy transfers (RET) with GSH-Au NCs@rGO (donor) could effectively quenched the ECL intensity to a reasonable range for requirements of trace analysis. The proposed ECL biosensing platform was evaluated with cardiac troponin I (cTnI) as a model analyte, achieving a low detection limit of 54.95 fg/mL. This strategy may provide as new approaches for the sensitive detection of biomarkers in the early clinical diagnosis of diseases.

Self-powered photoelectrochemical biosensor with inherent potential for charge carriers drive.

Self-powered photoelectrochemical (PEC) sensing platform without external voltage has provided a breakthrough in the development of biosensors, however, it is necessary to find suitable Fermi energy level difference between photoanode materials and photocathode materials as the driving force. Herein, the self-powered PEC sensor was developed to combine the advantages of both the photoanode (SnS2/In2S3) and the photocathode (CuInS2). The sufficient Fermi level differentiation between the photoanode with the photocathode not only resulted in an evident photocurrent response vis tuning the electron transfer but avoided redox reactions of extra electron donors/acceptors to enhance the accuracy of the sensor. The biological target was immobilized on the photocathode, which allowed the sensor to possess a good anti-interference capability for the detection of real samples. The proposed PEC sensor exhibits good sensitivity for the cytokeratin 19 fragment (CYFRA21-1) detection and a low limit of detection (LOD) of 6.57 fg mL-1. Moreover, the as-purposed PEC system with good anti-interference capability and accuracy has implications for the detection of other biomarkers.

A dual-signal output electrochemical immunosensor based on Au-MoS2/MOF catalytic cycle amplification strategy for neuron-specific enolase ultrasensitive detection.

In this work, a dual-signal output electrochemical immunosensor based on the Au-MoS2/MOF high-efficiency catalytic cycle amplification strategy for the sensitive detection of neuron-specific enolase (NSE). The mixed-valence structure MOF (Fe2+/Fe3+-MOF) exhibits high-speed charge mobility and excellent electrochemical performance. Notably, nanoflowers-like MoS2 (MoS2 NFs), as a co-catalyst, were introduced into Fe2+/Fe3+-MOF to successfully ensure the stable cycle of Fe2+/Fe3+ at the electrode interface. The constantly emerging of "fresh" active sites significantly amplified the current signal response. According to the electrochemical behavior, the catalytic cycle mechanism and electron transfer pathways between MoS2 and Fe2+/Fe3+-MOF were further discussed. The two output signals of a sample realized the self-calibration of the immunoassay results, which improved the reliability and sensitivity of the immunosensor. Under optimal conditions, the linear range was 1.00 pg/mL∼100 ng/mL, and the low detection limits were 0.37 pg/mL and 0.52 pg/mL. The results suggest that the as-proposed immunosensor will be promising in the biological analysis and early clinical diagnosis of cancer biomarkers.

An electrochemical amplification strategy based on the ferrocene functionalized cuprous oxide superparticles for the detection of NSE.

A sandwich-type electrochemical immunosensor was designed utilizing ferrocene-functionalized cuprous oxide superparticles (Au/Fc@CuxO SPs) as the signal label and graphene supported by hollow carbon balls (HCNs-GR) as the substrate. The CuxO SPs possess a superparticle structure with synergistic properties of isotropy and promising catalytic activity. Ferrocene (Fc) was deposited on the CuxO SPs to act as the electronic transmission medium. The Au/Fc@CuxO SPs played a pivotal role in improving the sensitivity of the immunosensor. The graphene supported by hollow carbon balls (HCNs-GR) was used to modify the electrode surface. The embedding of hollow carbon nanospheres (HCNs) reduced the decrease of the effective surface area caused by the stacking of graphene nanotubes. Meanwhile, the load of carbon balls further increases the surface area of graphene, enabled HCNs-GR to immobilize antibodies more effectively, improved the sensitivity of the immunosensor. The proposed immunosensor showed a linear range from 500 fg/mL to 100 ng/mL, with the detection limit to 25.7 fg/mL.

"Gold-plated" IRMOF-3 and sea cucumber-like Pd@PtRh SNRs based sandwich-type immunosensor for dual-mode detection of PCT.

Electrochemical immunoassays are often used in the detection of biomarkers, and their sensitivity depends on the nature of the substrate and the catalytic activity of the signal amplification platform. In this work, a novel sandwich-type signal amplification strategy with a "gold-plated" organometallic frame (Au/IRMOF-3) as the substrate and the sea cucumber-like Pd@PtRh trimetallic nanomaterial (Pd@PtRh SNRs) as label was fabricated. For the substrate, gold nanoparticles (Au NPs) are stably connected to the free amino groups on the surface of organometallic frame (IRMOF-3), which not only prevent the agglomeration of Au NPs, but also greatly enhance the conductivity of the nanocomposites. The synergy between the two nanomaterials further shows a stronger affinity for the fixation of capture antibodies (Ab1). For the label, the effective high catalytic activity comes from the Pd@PtRh SNRs with a sea cucumber-like morphology. The nano-scale spherical PtRh crystals epitaxially grown on smooth Pd nanorods (Pd NRs) have more catalytically active sites because of the abundant edge and corner atoms, resulting in high catalytic activity and durability towards H2O2 reduction. Choosing calcitonin (PCT) as the target, differential pulse voltammetry (DPV) and amperometric i-t dual-mode detection was used to demonstrate the feasibility of the immunosensor. The results confirmed that the immunosensor exhibits excellent analytical capabilities and is satisfied in the analysis of human serum samples. Therefore, this strategy has great potential in the clinical application of electrochemical immunosensors.

Separation of Biological Events from the Photoanode: Toward the Ferricyanide-Mediated Redox Cyclic Photoelectrochemical System of an Integrated Photoanode and Photocathode.

Photoanode sensing platforms with remarkable photoelectrochemical (PEC) response and satisfying visible-light absorption have become the most promising detection systems. Nevertheless, their inevitable electrophilic character limits their expansion in the bioassay because of reductive substances in serum or other body fluids that can severely interfere with the photocurrent to be read. To solve it, a PEC platform-assembled dual-active electrode is designed to realize the separation of biological monitoring from the photoanode. The ferricyanide ([Fe(CN)6]3-)-mediated redox cycle is first proposed to meet the gain and loss electron requirements of the PEC system. It can avoid the self-reaction in the electrolyte caused by the addition of a traditional electron donor and acceptor, for instance, ascorbic acid and hydrogen peroxide. As a consequence, the traditional counter electrode (Pt wire) is replaced by Fe2O3/AgInS2 heterojunction, which can amplify the PEC response of the cathode to meet the requirement of trace analysis. An aptasensor fabricated by the above strategies exhibits convincing data for 17ß-estradiol (E2) detection from which a wide detection range is obtained in 10 fg/mL to 1 µg/mL with a detection limit of 2.74 fg/mL (S/N = 3). These advanced elements show a rosy prospect for environmental monitoring and point-of-care biomarker diagnosis.

Intramolecular Photoelectrochemical System Using Tyrosine-Modified Antibody-Targeted Peptide as Electron Donor for Detection of Biomarkers.

An intramolecular photoelectrochemical (PEC) system is designed from the novel electron donor YYYHWRGWV (Y3-H) peptide ligand for the first time. The bifunctional nonapeptide cannot only rely on the HWRGWV sequence as a site-oriented immobilizer to recognize the crystallizable fragment (Fc) domains of the antibody but also acts as electron donors for PEC generation via three tyrosine (Y) of the N-terminal. The Bi2WO6/AgInS2 heterojunction with a significant visible-light absorption is utilized as a photoelectric generator, and the motivation is ascribed to a proven proposition, namely, that short-wavelength illuminant radiates proteins, causing a decline in bioactivity of immune protein. An innovative biosensor is fabricated using the above strategies for the detection of CYFRA21-1, a biomarker of squamous cell lung carcinoma. This sort of PEC-based sensing platform shows convincing experimental data and could be an effective candidate for clinical application in the future due to their extremely skillful conception.

Intramolecular Coreaction Accelerated Electrochemiluminescence of Polypeptide-Biomineralized Gold Nanoclusters for Targeted Detection of Biomarkers.

The development of label-free electrochemiluminescence (ECL)-based sensing technology for biomarkers detection has a congenital defect compared to noncompetitive sandwich-type biosensors due to the lack of detection antibody conjugated with a signal label. Nevertheless, it is still not difficult to realize the ultrasensitive analysis benefit from the exploration of efficient sensing substrates and signal transducers. In this work, an innovative sensing system is purposed utilizing Fe2O3 nanoarrays (Fe2O3 NAs) as a well-ordered coreaction accelerator and polypeptide-biomineralized gold nanoclusters (Au NCs) as a signal transducer. Bifunctional peptide ligands of H2N-MMYYHFRRHL-COOH (MYH-10) are self-designed; it cannot only play a role of reductant and coupling reagent for cluster formation using the MMYY sequence root in the N-terminal but also act as a connection for coupling carriers and immune molecules via the HFRRHL region of the C-terminal. In addition to intramolecular ECL emission between Au NCs and tris(3-aminoethyl)amine (TAEA), all strategies undoubtedly reduce the spatial hindrance of the sensing interface and increase the effectiveness of the electron transfer and immune recognition. With CYFRA21-1 as a target, the biosensor exhibits a linear ECL response in a wide range (10 fg mL-1 to ∼100 ng mL-1) and an ultralow detection limit of 1.33 fg mL-1 (S/N = 3). With convincing experimental data, these innovative strategies will be more eye-catching in peptide-based nanocluster synthesis and expansion of a more novel thought for sensing platform fabrication.

[Effects of organic manure on the profile distribution of soil nitrate-N in a peach orchard].

In 2004 and 2005, a field experiment was conducted in a peach orchard in Pinggu District of Beijing to study the effects of organic manure on the profile distribution of nitrate-N in soil. Four treatments were installed, i.e., applying 6.75 x 10(4) kg x hm(-2) of organic manure both in 2004 and in 2005 (T1), no fertilization in 2004 but applying 13.5 x 10(4) kg x hm(-2) of organic manure in 2005 (T2), no fertilization in 2004 but applying 6.75 x 10(4) kg x hm(-2) of organic manure in 2005 (CK), and no fertilization both in 2004 and in 2005 (CK). In 2006, soil samples at the depth of 0-120 cm were collected from the treatments and analyzed. The results showed that soil nitrate-N had a relatively uniform distribution in the profile in CK, accumulated more at the depth of 0-60 cm and decreased gradually at 60-120 cm in T1 and T3, and increased with increasing depth, with the peak at the depth of 100-120 cm in T2. The soil nitrate-N content below 60 cm in T2 was the highest among all the treatments, indicating that applying excessive amount of organic manure could induce nitrate-N leaching. The profile distribution of soil nitrate-N had significant correlations with the total amount of applied organic manure, the amount of organic manure applied in the nearest year, and the distance of sampling sites from peach tree. A correlation model of organic manure treatments and soil nitrate-N distribution was established.