Nickel nanoclusters as a novel emitter for molecularly imprinted electrochemiluminescence based sensor toward nanomolar detection of creatinine

Magnetic N-doped carbon derived from mixed ligands MOF as effective electrochemiluminescence coreactor for performance enhancement of SARS-CoV-2 immunosensor

COVID-19 as an infectious disease with rapid transmission speed is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), so, early and accurate diagnostics of COVID-19 is quite challenging. In this work, the selective and sensitive self-enhanced ECL method to detect of SARS-CoV-2 protein was designed with magnetic N-doped carbon derived from dual-ligand metal-organic frameworks (MOF) (CoO@N-C) with the primary and tertiary amino groups as a novel coreactant that covalently combined with Ru(bpy)2(phen-NH2)2+ as electrochemiluminescence (ECL) emitter. Mixed-ligand strategy and selected nitrogen-containing ligands, 4,4',4''-((1,3,5-triazine-2,4,6-triyl) tris-(azanediyl)) tribenzoic acid (H3TATAB) with 2-aminoterephthalic acid (BDC-NH2) were used for synthesis of the proposed MOF. Also, magnetic CoO@N-C with high synergistically charge transfer kinetics and good stability can be used as an effective platform/coreactor on the ITO electrode which load more Ru-complex as signal producing compound and SARS-CoV-2 N protein antibody to increase the sensitivity of the immunosensor. Furthermore, (CoO@N-C) as coreactor improved the ECL signal of the Ru (II)-complex more than 2.1 folds compared to tripropylamine. In view of these competences, the novel "on-off" ECL biosensor performed with great stability and repeatability for detection of SARS-CoV-2 protein, which exhibited a broad linearity from 8 fg. mL-1 to 4 ng. mL-1 (6 order of magnitude) and an ultra-low limit of detection 1.6 fg. mL-1. Finally, this proposed method was successfully applied to detect of SARS-CoV-2 N protein in serum sample with satisfactory results, indicating the proposed immunosensor has the potential for quick analysis of SARS-CoV-2.

Recent Advances in Electroluminescent Metallic Nanoclusters: From Materials to Devices

Metallic nanoclusters (MNCs) were developed rapidly in recent decades, owing to their unique electronic structures and excited state characteristics, leading to their wide applications. Luminescence as one of the most important functions for MNCs has also been used to realize biodetection, displays, and lighting, through either electrochemiluminescence (ECL) or electroluminescence (EL). Both emissive properties and electrochemical activities of MNCs were utilized to enhance ECL and EL through facilitating exciton formation and radiation, rendering the rapid emerging of the latter in the last ten years. Through ligand modification, radiative excited-state components were increased to realize state-of-the-art photo- and electroluminescence efficiencies up to ∼100% and ∼30%, as well as ultralow biodetection limits. Nonetheless, material selection space and processing technologies are still limited. Herein, we overview and discuss recent advances of MNCs-based ECL and EL, through both aspects of materials/systems and devices, which would enlighten continuous innovations in optoelectronic MNCs.

Dual-source signal amplification electrochemiluminescence sensor combined with molecularly imprinted polymers for the imidacloprid detection

A novel lanthanide metal-organic-gel (MOG)-derived material/nitrogen-doped graphdiyne (Tb-Ru-MOG/CeO2/N-GDY) composite with a dual-source signal amplification strategy was prepared and used to construct a molecularly imprinted sensor based on bifunctional monomers for the detection of imidacloprid (IMI) using electrochemiluminescence (ECL). In a green reaction environment, terbium (III) (Tb3+) can undergo multiple coordination reactions with 4'-(4-carboxyphenyl)-2,2':6',2″-terpyridine (Hcptpy) and tris(4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium (II) dichloride (Ru(dcbpy)32+), and combine with ceria nanoparticles (CeO2 NPs) to form Tb-Ru-MOG/CeO2. Within the Tb-Ru-MOG/CeO2 framework, energy transfer from the double ligands can sensitize the central Tb3+, triggering a distinct antenna effect and energy-transfer, and its polyporous configuration offered a nanoconfined space for Ce3+/Ce4+ to effectively catalyze coreactant radicals (S2O82-), leading to in-situ endogenous activation ECL reactions. The conductive N-GDY accelerated electron movement and increased the loading on the electrode surface, enhancing the exogenous excitation of the ECL signals. Leveraging the synergistic effect of the bifunctional monomer, the synthesized molecularly imprinted polymers (MIPs) ECL sensor demonstrated a wide detection range from 10 nM to 10,000 nM for IMI, with a limit of detection (LOD) of 1.37 nM, showcasing an innovative concept for the dual-source strategy of signal amplification in integrated ECL composites to analyze food and environmental hazards.

Protein-Templated Metal Nanoclusters: Molecular-like Hybrids for Biosensing, Diagnostics and Pharmaceutics

The use of proteins as biomolecular templates to synthesize atomically precise metal nanoclusters has been gaining traction due to their appealing properties such as photoluminescence, good colloidal- and photostability and biocompatibility. The synergistic effect of using a protein scaffold and metal nanoclusters makes it especially attractive for biomedical applications. Unlike other reviews, we focus on proteins in general as the protective ligand for various metal nanoclusters and highlight their applications in the biomedical field. We first introduce the approaches and underlined principles in synthesizing protein-templated metal nanoclusters and summarize some of the typical proteins that have been used thus far. Afterwards, we highlight the key physicochemical properties and the characterization techniques commonly used for the size, structure and optical properties of protein-templated metal nanoclusters. We feature two case studies to illustrate the importance of combining these characterization techniques to elucidate the formation process of protein-templated metal nanoclusters. Lastly, we highlight the promising applications of protein-templated metal nanoclusters in three areas-biosensing, diagnostics and therapeutics.

Low-Triggering-Potential Single-Color Electrochemiluminescence from Bovine Serum Albumin-Stabilized Unary Au Nanocrystals for Immunoassays

Herein, low-triggering-potential (LTP) electrochemiluminescence (ECL) with an onset around 0.0 V (vs Ag/AgCl) is proposed with bovine serum albumin (BSA)-stabilized Au nanocrystals (BSA-AuNCs) as a luminophore and hydrazine hydrate (N₂H₄) as a coreactant. The BSA-AuNCs/N₂H₄ system can exhibit efficient LTP-ECL around 0.37 V with the luminophore of both monodispersed and surface-confined states. The LTP-ECL of BSA-AuNCs/N₂H₄ is a kind of single-color emission with a maximum emission wavelength around 740 nm, which is obviously red-shifted for 80 nm from that of BSA-AuNCs PL, and indicates that the ECL is generated in a surface-defect-involved route instead of the band-gap-engineered route. Importantly, BSA-AuNCs can be utilized as ECL tags to perform sandwich-type immunoassays with acceptable sensitivity and selectivity, which exhibits a wide linear response for determining CA125 from 0.5 to 1000 mU/mL and a limit of detection of 0.05 mU/mL (S/N = 3).

Alkaline n-gqds fluorescent probe for the ultrasensitive detection of creatinine

Creatinine (Crn) is an important excretory product of the human body. Medical laboratory technology has improved over years and brought many advancements in clinical diagnostics equipment, and testing techniques and made the tests more efficient. Yet, the quantitative analysis of Crn is still carried out by the classical Jaffe's reaction (using Picric acid (PA) with NaOH) method. Since PA is hazardous to human health, alternative solutions such as; nanoparticles and surface-modified nanoparticles can be used. Exploring the optoelectronic properties of carbon-based quantum dots for biomolecule sensing is of current interest among researchers. Nitrogen functionalized graphene quantum dots (Alk-NGQDs) measured featured Crn easier and reduced the time taken for the test carried out in laboratories. The synthesized Alk-NGQDs optical, structural, morphological properties, surface and compositions are studied through XPS, HRTEM, XRD, FTIR, and spectroscopic techniques. Alk-NGQDs at alkaline conditions (pH 9.5) form a stable complex with Crn through intermolecular charge transfer (ICT). The fluorescence titration method is used to sense Crn in commercial Crn samples and human blood serum. To understand the efficacy of sensing creatinine using Alk-NGQDs, working concentration, fluorescence quantum yield, the limit of detection, and quenching constant are calculated using the Stern-Volmer plot. The emission property of Alk-NGQDs is aimed to bring an alternative to the traditional colorimetric Jaffe's reaction.

Recent progress of metal nanoclusters in electrochemiluminescence

Metal nanoclusters (MeNCs), composed of a few to hundreds of metal atoms and appropriate surface ligands, have attracted extensive interest in the electrochemiluminescence (ECL) realm owing to their molecule-like optical, electronic, and physicochemical attributes and are strongly anticipated for discrete energy levels, fascinating electrocatalytic activity, and good biocompatibility. Over the past decade, huge efforts have been devoted to the synthesis, properties, and application research of ECL-related MeNCs, and this field is still a subject of heightened concern. Therefore, this perspective aims to provide a comprehensive overview of the recent advances of MeNCs in the ECL domain, mainly covering the emerged ECL available MeNCs, unique chemical and optical properties, and the general ECL mechanisms. Synthesis strategies for desirable ECL performance are further highlighted, and the resulting ECL sensing applications utilizing MeNCs as luminophores, quenchers, and substrates are discussed systematically. Finally, we anticipate the future prospects and challenges in the development of this area.

Recent Advances of Nanomaterials-Based Molecularly Imprinted Electrochemical Sensors

Molecularly imprinted polymer (MIP) is illustrated as an analogue of a natural biological antibody-antigen system. MIP is an appropriate substrate for electrochemical sensors owing to its binding sites, which match the functional groups and spatial structure of the target analytes. However, the irregular shapes and slow electron transfer rate of MIP limit the sensitivity and conductivity of electrochemical sensors. Nanomaterials, famous for their prominent electron transfer capacity and specific surface area, are increasingly employed in modifications of MIP sensors. Staying ahead of traditional electrochemical sensors, nanomaterials-based MIP sensors represent excellent sensing and recognition capability. This review intends to illustrate their advances over the past five years. Current limitations and development prospects are also discussed.

A copper nanoclusters probe for dual detection of microalbumin and creatinine

A fluorescent probe based on glutathione-capped copper nanoclusters (GSH-CuNCs) was developed for the detection of dual targets, human serum albumin (HSA) and creatinine, in human urine. The GSH-CuNCs were synthesized by a one-pot green method using ascorbic acid as a reducing agent. The detection of HSA was in a turn-on mode via electrostatic interaction in a basic condition while the detection of creatinine was in a turn-off mode via non-covalent bonding in an acidic condition. Under optimal conditions, the linear range and detection limit of HSA were 5.0 nM to 150 nM and 1.510 ± 0.041 nM, while those of creatinine were 30 μM to 1000 μM and 13.0 ± 1.0 μM. This easily fabricated nanocluster probe provided a fast response with high sensitivity, and good selectivity. Recoveries from urine samples were in the range of 81.44 ± 0.25 to 109.22 ± 0.57% for HSA and 80.57 ± 0.16 to 109.0 ± 0.10% for creatinine. The urinary analytical results from the fluorescent probe were in good agreement (P > 0.05) to those obtained from immunoturbidimetric and enzymatic methods, signifying the excellent performance of this sensing system.

Ultrasensitive electrochemiluminescence sensor based on perovskite quantum dots coated with molecularly imprinted polymer for prometryn determination

A highly effective molecularly imprinted electrochemiluminescence sensor was constructed for prometryn determination in environmental and biological samples by using perovskite quantum dots coated with a molecularly imprinted silica layer (MIP/CsPbBr₃-QDs) as the recognition and response element. MIP/CsPbBr₃-QDs were immobilized on a glassy carbon electrode (GCE) through electropolymerization, and the electrochemiluminescence (ECL) response of MIP/CsPbBr₃-QDs could be motivated under the condition of H₂O₂ as co-reactant. ECL signal was selectively quenched with prometryn by hindering electron transfer and directly proportional to the logarithm of prometryn concentration (0.10-500.0 μg/L) with a correlation coefficient of 0.9960. Limits of detection in fish and seawater samples were 0.010 μg/kg and 0.050 μg/L, respectively. Excellent recoveries of 88.0%-106.0% were acquired for fish and seawater samples with a relative standard deviation below 4.2%. The constructed MIECL sensor based on MIP/CsPbBr₃-QDs showed good stability, accuracy, and precision for sensitive detection of prometryn in aquaculture products and environmental samples.

Application progress of magnetic molecularly imprinted polymers chemical sensors in the detection of biomarkers

Specific recognition and highly sensitive detection of biomarkers play an essential role in identification, early diagnosis and prevention of many diseases. Magnetic molecularly imprinted polymers (MMIPs) have been widely used to capture biomimetic receptors for targets in various complex matrices due to their superior recognition ability, structural stability, and rapid separation characteristics, which overcome the existing deficiencies of traditional recognition elements such as antibodies, aptamers. The integration of MMIPs as recognition elements with chemical sensors opens new opportunities for the development of advanced analytical devices with improved selectivity and sensitivity, shorter analysis time, and lower cost. Recently, MMIPs-chemical sensors (MMIPs-CS) have made significant progress in detection, but many challenges and development spaces remain. Therefore, this review focuses on the research progress of the sensor based on biomarker detection and introduces the surface modification of the magnetic support material used to prepare high selective MMIPs, as well as the selective extraction of target biomarkers by MMIPs from the complex biological sample matrix. Based on the understanding of optical sensors and electrochemical sensors, the applications of MMIPs-optical sensors (MMIPs-OS) and MMIPs-electrochemical sensors (MMIPs-ECS) for biomarker detection were reviewed and discussed in detail. Moreover, it provides an overview of the challenges in this research area and the potential strategies for the rational design of high-performance MMIPs-CS, accelerating the development of multifunctional MMIPs-CS.

Ultrasensitive Glutathione-Mediated Facile Split-Type Electrochemiluminescence Nanoswitch Sensing Platform

Seeking for an advanced electrochemiluminescence (ECL) platform is still an active and continuous theme in the ECL-sensing realm. This work outlines a femtomolar-level and highly selective glutathione (GSH) and adenosine triphosphate (ATP) ECL assay strategy using a facile split-type gold nanocluster (AuNC) probe-based ECL platform. The system utilizes GSH as an efficient etching agent to turn on the MnO₂/AuNC-based ECL nanoswitch platform. This method successfully achieves an ultrasensitive detection of GSH, which significantly outperformed other sensors. Based on the above excellent results, GSH-related biological assays have been further established by taking ATP as a model. Combined with the high catalytic oxidation ability of DNAzyme, this ECL sensor can realize ATP assay as low as 1.4 fmol without other complicated exonuclease amplification strategies. Thus, we successfully achieved an ultrahigh sensitivity, extremely wide dynamic range, great simplicity, and strong anti-interference detection of ATP. In addition, the actual sample detection for GSH and ATP exhibits satisfactory results. We believe that our proposed high-performance platform will provide more possibilities for the detection of other GSH-related substances and show great prospect in disease diagnosis and biochemical research.

Selective detection of enrofloxacin in biological and environmental samples using a molecularly imprinted electrochemiluminescence sensor based on functionalized copper nanoclusters

Enrofloxacin (ENR) is a broad-spectrum fungicide that has been largely applied in pharmacy and animal-specific medicine. In this paper, a simple, novel and highly sensitive molecularly imprinted electrochemiluminescence (MIP-ECL) sensor based on mercaptopropionic acid-functionalized copper nanoclusters (MPA-Cu NCs) was developed to selectively detect enrofloxacin (ENR). MPA-Cu NCs prepared by a one-step method were used to modify the glassy carbon electrode. A molecularly imprinted polymer film containing the cavity was constructed after electropolymerization and elution. Under optimized conditions, the MIP-ECL sensor could detect ENR in the range of 0.1 nM-1 μM (R² = 0.9863) with a low limit of detection of 27 pM, and the recovery rates of ENR in biological and lake water samples were 88.20-105.0%. The MIP-ECL sensor provided path to improve the stability issues of Cu NCs, which might open promising avenues to develop new ECL systems for biological analysis and environmental water monitoring.

Graphdiyne nanosheet as a novel sensing platform for self-enhanced electrochemiluminescence of MOF enriched ruthenium (II) in the presence of dual co-reactants for detection of tumor marker

Graphdiyne (GDY) is a new two-dimensional carbon material with high charge carrier mobility, excellent conductivity, more suitable band gap, and natural pores was introduced as a new electrochemiluminescent sensing platform. Herein, the metal organic framework (MOFs) used for enrichment of luminophore with grafting Ru(bpy)₂(phen-NH₂)²⁺(Ru-complex) and Ru-complex amine-rich nitrogen-doped carbon nanodots(Ru-NCNDs) via both encapsulating and external decoration and decoration of SmS₂ QDs as coreactant. Then, the MOF enriched Ru-complex (Ru@MOF@NCNDs-Ru@SmS₂ QD) located on a GDY modified ITO electrode developed as a novel and efficient ECL platform. According to the Density Functional Theory (DFT) calculation, the band gap of graphdiyne/Ru(bpy)₂(phen-NH₂)²⁺ system decreased compared to graphdiyne, Ru-complex and also graphene oxide/Ru(bpy)₂(phen-NH₂)²⁺system, which enhanced (2 folds) the signal response of the presented ECL platform. The ECL response signal of the suggested emitter with high ECL efficiency (13.34%) increased 8 and 4 folds compared to GDY/Ru-NCNDs and GDY/Ru@MOF@NCNDs-Ru as platforms, respectively. The proposed ECL platform applied for CA19-9 antigens detection at concentration range 0.0005 UmL^-1 to 200 UmL^-1 and detection limit of 0.00013 UmL^-1.The development of GDY based platform for decorating nano luminophores, not only provides the design of ECL luminophores with high performance but also promises the application of the presented strategy for fabrication of ultrasensitive bio affinity sensors as candidates in clinical monitoring and diseases diagnostics.

A review of recent advances in non-enzymatic electrochemical creatinine biosensing

Creatinine biosensing is a rapidly developing field owing to the clinical relevance of creatinine as a vital biomarker for several diseases associated with renal, thyroidal, and muscular dysfunctions. Over the years, we have observed numerous creatinine biosensing strategies, including the most widely studied enzymatic creatinine biosensors. Though the enzymatic approach provides excellent selectivity and reliability, it has certain drawbacks, which include high fabrication cost and poor storage stability (that is inherent to every enzyme-based biosensors). This has led to the development of non-enzymatic creatinine biosensors, of which electrochemical sensors are the most promising for point-of-care applications. However, only a limited number of studies have been conducted and there is a lack of reviews addressing the recent advances in this research area. Herein, we present for the first time, a review with a prime focus on the various strategies implemented in non-enzymatic electrochemical creatinine biosensing. We aim to offer a comprehensive context on the achievements and limitations of currently available non-enzymatic electrochemical creatinine biosensors and address the underlying factors pertaining to the interplay of modification/fabrication techniques with the sensitivity, selectivity, interferences, and long-term storage stability of the biosensor. We hope that this work shall prove to be seminal in the conception and advancement of future non-enzymatic electrochemical creatinine biosensors.

Trend in creatinine determining methods: Conventional methods to molecular‐based methods

Renal failure (RF) disease is ranked as one of the most prevalent diseases with severe morbidity and mortality. Early diagnosis of RF leads to subsequent control of disease to reduce the poor prognosis. The level of sera creatinine is considered as a significant biomarker for kidney biofunction, which is routinely detected by the Jaffe reaction. The normal range for creatinine in the blood may be 0.84‐1.21 mg/dL. Low accuracy, insufficient sensitivity, explosive and toxicity of picric acid, and pseudo‐interaction with nonspecific elements such as ammonium ions in the Jaffe method lead to the development of various techniques for precise detection of creatinine such as spectroscopic, electrochemical, and chromatography approaches and sensors based on enzymes, molecular imprinted polymer and nanoparticles, etc. Based on previously established results, they are trying to construct sensors with high accuracy, optimum sensitivity, acceptable linear/calibration range, and limit of detection, which are small in size and applicable by the patient him/herself (point‐of‐care testing). By comparing the results of research, a molecularly imprinted electrochemiluminescence‐based sensor with linear/calibration range of 5‐1 mMconcentration of creatinine and the detection limit of 0.5 nM has the best detectable resolution with 2 million measurable points. In this paper, we will review the recently developed methods for measuring creatinine concentration and renal biofunction.

Ultrasensitive molecularly imprinted fluorescence sensor for simultaneous determination of CA125 and CA15-3 in human serum and OVCAR-3 and MCF-7 cells lines using Cd and Ni nanoclusters as new emitters

In the clinical diagnosis of tumors, a single-marker immunoassay may lead to false results. Thus there is a need for an effective and valid method for the simultaneous measurement of multiple tumor markers. In this work, an efficient fluorescence immunosensor for the simultaneous measurement of CA125 and CA15-3 tumor markers was fabricated by utilizing the high selectivity of magnetic molecularly imprinted polymers (MMIPs) and the high sensitivity of a fluorescence (FL) method. Ni nanoclusters (Ni NCs) and noble Cd nanoclusters (Cd NCs) were introduced as efficient and economic emitters, and magnetic graphene oxide (GO-Fe₃O₄) was applied as a support material for surface molecularly imprinted polymers. Under the most favorable experimental conditions, the fluorescence intensity of the Cd NCs and Ni NCs gradually increased with increasing concentration of CA125 and CA15-3 antigens at a range of 0.0005-40 U mL^-1, respectively, with a limit of detection (LOD) of 50 μU mL^-1. The developed method had excellent properties including a broad linear range, good reproducibility, and simple operation for the clinical diagnosis of CA 125 and CA 15-3 tumor markers. This molecularly imprinted fluorescence sensor has the potential to be an effective clinical tool for the timely screening of breast cancer in human serum samples and OVCAR-3 and MCF-7 cell lines, and can be applied in clinical diagnostics.

Quantitative determination of creatinine from serum of prostate cancer patients by N-doped porous carbon antimony (Sb/NPC) nanoparticles

Creatinine is an indicator of hindrance in urination and renal insufficiency. Creatinine levels are the marker of the late stages of prostate cancer. Early and sensitive detection of creatinine can reduce deaths associated with prostate cancer. In this work, nitrogen-doped porous carbon antimony (Sb/NPC) nanoparticles are fabricated to be employed as a non-enzymatic biosensor. Sb/NPC has promising redox activity and is synthesized by a two-step reaction using low-cost precursors. Electrochemical sensing by Sb/NPC is conducted for standard creatinine solutions on a three-electrodes system. Cyclic voltammetry, amperometry, and electrochemical impedance spectroscopy are used to sense creatinine. LOD and LOQ of the Sb/NPC modified electrode are 0.74 µM and 2.4 µM, respectively. This electrode system analyzes creatinine in the serum of prostate cancer patients who have elevated PSA levels. More than 90% creatinine is recovered from a spiked serum sample of a prostate cancer patient. A direct relation is observed between PSA levels and creatinine levels in prostate cancer. The developed cyclic voltammetric setup detects trace concentrations of creatinine in serum.

A novel molecularly imprinted electrochemiluminescence sensor based on cobalt nitride nanoarray electrode for the sensitive detection of bisphenol S

A substitute for bisphenol A (BPA), bisphenol S (BPS) has endocrine disruptive and toxic effects and could pose potential risk on human health and the environment. Herein, we fabricated a sensitive molecularly imprinted electrochemiluminescence (MIECL) sensor for the determination of BPS. CoN nanoarray with outstanding electrical conductivity was prepared and it directly served as the sensor platform. Especially, due to the high surface area of the porous CoN nanoarray, the ECL probe of Ru(bpy)3 2+ could be absorbed on the electrode. By means of the cation exchange of Nafion membrane and utilizing tripropylamine (TPrA) as co-reactant, boosted ECL signals were obtained. Meanwhile, by combining with molecularly imprinted polymers (MIPs), the constructed sensor achieved specific recognition of BPS. On the basis of the superior properties of the CoN nanoarray-based electrode, the ECL signal of the proposed sensor was linearly proportional to the BPS concentration from 2.4 × 10-9 to 5.0 × 10-5 mol L-1 (R 2 = 0.9965) with a low limit of detection (LOD) of 8.1 × 10-10 mol L-1 (S/N = 3). To test the accuracy of the proposed method, the HPLC method was adopted to analyze drinking water samples as a comparison. The t-test result proved that discrepancies between HPLC analysis and the method using the fabricated MIECL sensor were acceptable. The developed MIECL sensor with the sensitive, selective, reproducible, and stable analytical performance provides a potential pathway for the detection of BPS and other BPA substitutes in drinking water samples.

Recent Advances in Electrochemiluminescence and Chemiluminescence of Metal Nanoclusters

Metal nanoclusters (NCs), including Au, Ag, Cu, Pt, Ni and alloy NCs, have become more and more popular sensor probes with good solubility, biocompatibility, size-dependent luminescence and catalysis. The development of electrochemiluminescent (ECL) and chemiluminescent (CL) analytical methods based on various metal NCs have become research hotspots. To improve ECL and CL performances, many strategies are proposed, from metal core to ligand, from intermolecular electron transfer to intramolecular electron transfer. Combined with a variety of amplification technology, i.e., nanostructure-based enhancement and biological signal amplification, highly sensitive ECL and CL analytical methods are developed. We have summarized the research progresses since 2016. Also, we discuss the current challenges and perspectives on the development of this area.

Highly Selective Electrochemiluminescence Sensor Based on Molecularly Imprinted-quantum Dots for the Sensitive Detection of Cyfluthrin

A highly selective and sensitive molecularly imprinted electrochemiluminescence (MIECL) sensor was developed based on the multiwall carbon nanotube (MWCNT)-enhanced molecularly imprinted quantum dots (MIP-QDs) for the rapid determination of cyfluthrin (CYF). The MIP-QDs fabricated by surface grafting technique exhibited excellent selective recognition to CYF, resulting in a specific decrease of ECL signal at the MWCNT/MIP-QD modified electrode. Under optimal conditions, the MIECL signal was proportional to the logarithm of the CYF concentration in the range of 0.2 µg/L to 1.0 × 10³ µg/L with a determination coefficient of 0.9983. The detection limit of CYF was 0.05 µg/L, and good recoveries ranging from 86.0% to 98.6% were obtained in practical samples. The proposed MIECL sensor provides a novel, rapid, high sensitivity detection strategy for successfully analyzing CYF in fish and seawater samples.

Magnetic molecularly imprinted electrochemical sensors: A review

The preparation and practical applications of molecularly imprinted electrochemical sensors (MIECSs) remain challenging due to issues involving electrode surface renewal modes, low adsorption capacities, and sample preparation speeds. To solve these issues, magnetic molecularly imprinted electrochemical sensors (MMIECSs) have been extensively explored by various groups. Recently, MMIECSs fabricated based on diverse strategies have yielded insight into the development of MIECSs, and they have provided effective paths for sample preparation, immobilization and renewal of molecularly imprinted polymers (MIPs) on the electrode surface, leading to promising performances of MIECSs. This review comprehensively describes the research advances for various types of MMIECSs and their applications in the fields of food safety, environmental monitoring, and clinical and pharmaceutical analysis. Based on our understanding of MMIECSs, the literature in this field is thoroughly explored and classified in this review. The challenges existing in this research area and some potential strategies for the rational design of high-performance MMIECS are also outlined.

Functional Magnetic Graphene Composites for Biosensing

Magnetic graphene composites (MGCs), which are composed of magnetic nanoparticles with graphene or its derivatives, played an important role in sensors development. Due to the enhanced electronic properties and the synergistic effect of magnetic nanomaterials and graphene, MGCs could be used to realize more efficient sensors such as chemical, biological, and electronic sensors, compared to their single component alone. In this review, we first reviewed the various routes for MGCs preparation. Then, sensors based on MGCs were discussed in different groups, including optical sensors, electrochemical sensors, and others. At the end of the paper, the challenges and opportunities for MGCs in sensors implementation are also discussed.

A highly sensitive sensor based on a computer-designed magnetic molecularly imprinted membrane for the determination of acetaminophen

In this paper, a sensor based on a magnetic surface molecularly imprinted membrane (MMIP) was prepared for the highly sensitive and selective determination of acetaminophen (AP). Before the experiment, the appropriate functional monomers and solvents required for the polymer were screened, and the molecular electrostatic potentials (MEPs) were calculated by the DFT/B3LYP/6-31 + G method. MMIP with high recognition of AP was synthesized based on Fe₃O₄@SiO₂nanoparticles (NPs) with excellent core-shell structure. Next, a carbon paste electrode (CPE) was filled with a piece of neodymium-iron-boron magnet to make magnetic electrode (MCPE), and MMIP/MCPE sensor was obtained by attaching a printed polymer to the surface of the electrode under the strong magnetic. Due to the stable molecular structure of the electrode surface, the sensor is highly effective and accurate for detection of AP using DPV. The DPV response of the sensor exhibited a linear dependence on the concentration of AP from 6 × 10^-8 to 5 × 10^-5 mol L^-1 and 5 × 10^-5 to 2 × 10^-4 mol L^-1, with a detection limit based on the lower linear range of 1.73 × 10^-8 mol L^-1(S/N = 3). When used for determination of AP in actual samples, the recovery of the sensor to the sample was 95.80-103.76%, and the RSD was 0.78%-3.05%.

Highly Sensitive and Selective Colorimetric Detection of Creatinine Based on Synergistic Effect of PEG/Hg2+-AuNPs

A colorimetric sensor, based on the synergistic coordination effect on a gold nanoparticle (AuNP) platform has been developed for the determination of creatinine. The sensor selects citrate stabilized AuNPs as a platform, polyethylene glycol (PEG) as a decorator, and Hg²⁺ as a linkage to form a colorimetric probe system (PEG/Hg²⁻–AuNPs). By forming hydrogen bond between the oxygen-containing functional groups of PEG and citrate ions on the surface of AuNPs, this probe shows good stability. PEG coordinated with Hg²⁺ synergistically and specifically on the surface of dispersed AuNPs, and the existence of creatinine could induce the aggregation of AuNPs with a corresponding color change and an obvious absorption peak shift within 5 min. This PEG/Hg²⁺–AuNPs probe towards creatinine shows high sensitivity, and a good linear relationship (R² = 0.9948) was obtained between A_{620–522 nm} and creatinine concentration, which can achieve the quantitative calculations of creatinine. The limit of detection (LOD) of this PEG/Hg2+–AuNPs probe was estimated to be 9.68 nM, lower than that of many other reported methods. Importantly, the sensitive probe can be successfully applied in a urine simulating fluid sample and a bovine serum sample. The unique synergistic coordination sensing mechanism applied in the designation of this probe further improves its high selectivity and specificity for the detection of creatinine. Thus, the proposed probe may give new inspirations for colorimetric detection of creatinine and other biomolecules.

Preparation and applications of electrochemical chemosensors based on carbon-nanomaterial-modified molecularly imprinted polymers

The past few decades have witnessed a rapid development in electrochemical chemosensors (ECCSs). The integration of carbon nanomaterials (CNMs) and molecularly imprinted polymers (MIPs) has endowed ECCSs with high selectivity and sensitivity toward target detection. Due to the integrated merits of MIPs and CNMs, CNM-modified MIPs as ECCSs have been widely reported and have excellent detection applications. This review systematically summarized the general categories, preparation strategies, and applications of ECCSs based on CNM-modified MIPs. The categories include CNM-modified MIPs often hybridized with various materials and CNM-encapsulated or CNM-combined imprinting silica and polymers on working electrodes or other substrates. The preparation strategies include the polymerization of MIPs on CNM-modified substrates, co-polymerization of MIPs and CNMs on substrates, drop-casting of MIPs on CNM-modified substrates, self-assembly of CNMs/MIP complexes on substrates, and so forth. We discussed the in situ polymerization, electro-polymerization, and engineering structures of CNM-modified MIPs. With regard to potential applications, we elaborated the detection mechanisms, signal transducer modes, target types, and electrochemical sensing of targets in real samples. In addition, this review discussed the present status, challenges, and prospects of CNM-modified MIP-based ECCSs. This comprehensive review is desirable for scientists from broad research fields and can promote the further development of MIP-based functional materials, CNM-based hybrid materials, advanced composites, and hybrid materials.

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.

Molecularly Imprinted Polymer-Based Hybrid Materials for the Development of Optical Sensors

We report on the development of new optical sensors using molecularly imprinted polymers (MIPs) combined with different materials and explore the novel strategies followed in order to overcome some of the limitations found during the last decade in terms of performance. This review pretends to offer a general overview, mainly focused on the last 3 years, on how the new fabrication procedures enable the synthesis of hybrid materials enhancing not only the recognition ability of the polymer but the optical signal. Introduction describes MIPs as biomimetic recognition elements, their properties and applications, emphasizing on each step of the fabrication/recognition procedure. The state of the art is presented and the change in the publication trend between electrochemical and optical sensor devices is thoroughly discussed according to the new fabrication and micro/nano-structuring techniques paving the way for a new generation of MIP-based optical sensors. We want to offer the reader a different perspective based on the materials science in contrast to other overviews. Different substrates for anchoring MIPs are considered and distributed in different sections according to the dimensionality and the nature of the composite, highlighting the synergetic effect obtained as a result of merging both materials to achieve the final goal.

Nitrogen-terminated silicon nanoparticles obtained via chemical etching and passivation are specific fluorescent probes for creatinine

A method is described here to prepare water-dispersible nitrogen-functionalized silicon nanoparticles (N-SiNPs). It consists of two steps, viz. etching of the oxidized shell of SiNPs and nitrogen-passivation of the exposed silicon. The resulting N-SiNPs have an average diameter of 2.6±0.7 nm and show blue fluorescence (with excitation/emission peaks at 340/420 nm). The fluorescence quantum yield is 23% and the decay time is in the nanosecond regime. Compared to etching methods using a plasma or hydrofluoric acid, the process described here (etching and passivation) is mild, continuous, fast, and air-compatible. The N-SiNPs modified with chlorotetracycline are shown to be a viable fluorescent probe for creatinine. Fluorescence drops in the 0 to 20 μM creatinine concentration range, and the limit of detection is 0.14 μM.

Modern creatinine (Bio)sensing: Challenges of point-of-care platforms

The importance of knowing creatinine levels in the human body is related to the possible association with renal, muscular and thyroid dysfunction. Thus, the accurate detection of creatinine may indirectly provide information surrounding those functional processes, therefore contributing to the management of the health status of the individual and early diagnosis of acute diseases. The questions at this point are: to what extent is creatinine information clinically relevant?; and do modern creatinine (bio)sensing strategies fulfil the real needs of healthcare applications? The present review addresses these questions by means of a deep analysis of the creatinine sensors reported in the literature over the last five years. There is a wide range of techniques for detecting creatinine, most of them based on optical readouts (20 of the 33 papers collected in this review). However, the use of electrochemical techniques (13 of the 33 papers) is recently emerging in alignment with the search for a definitive and trustworthy creatinine detection at the point-of-care level. In this sense, biosensors (7 of the 33 papers) are being established as the most promising alternative over the years. While creatinine levels in the blood seem to provide better information about patient status, none of the reported sensors display adequate selectivity in such a complex matrix. In contrast, the analysis of other types of biological samples (e.g., saliva and urine) seems to be more viable in terms of simplicity, cross-selectivity and (bio)fouling, besides the fact that its extraction does not disturb individual's well-being. Consequently, simple tests may likely be used for the initial check of the individual in routine analysis, and then, more accurate blood detection of creatinine could be necessary to provide a more genuine diagnosis and/or support the corresponding decision-making by the physician. Herein, we provide a critical discussion of the advantages of current methods of (bio)sensing of creatinine, as well as an overview of the drawbacks that impede their definitive point-of-care establishment.

A molecularly imprinted electrochemiluminescence sensor for ultrasensitive HIV-1 gene detection using EuS nanocrystals as luminophore

Development of simple, sensitive and specific method for human immunodeficiency virus (HIV) assays are urgently demand. In this study, we developed a novel molecularly imprinted polymer (MIP) electrochemiluminescence (MIP-ECL) sensor for the highly sensitive and selective HIV-1 gene detection using Europium sulfide nanocrystals (EsNCs) as signal producing compound. Here, the HIV aptamer as the template and o-phenylenediamine as the functional monomer, were electropolymerized directly on the surface of ITO electrode. With the hybridization reaction between the assemblies of EuS NCs functionalized 5-amino-labeled oligonucleotides as capture probes and oligonucleotides as detection target (HIV gene), the ECL signal significantly increased using K₂S₂O₈ as coreactant. Taking advantage of both MIP-ECL assays and the strong electrochemiluminescence emission of EuS NCs, the sensitive and selective HIV gene detection has been achieved in a linear range 3.0 fM to 0.3 nM with a detection limit of 0.3 fM. The present MIP-ECL biosensor showed good specificity for HIV DNA detection compared to non-complementary and two bases mismatched sequences. The proposed ECL biosensor was applied to detect of HIV DNA in real human serum samples and satisfactory results were obtained. Due to high sensitivity and selectivity, excellent reproducibility and stability of the proposed assay, EuS NCs can be used as novel luminophore for development of MIP-ECL sensors for detection of other DNA biomarkers.