Cu/Mn Double-Doped CeO2 Nanocomposites as Signal Tags and Signal Amplifiers for Sensitive Electrochemical Detection of Procalcitonin

Molecularly imprinted polymer-based electrochemical sensor for rapid detection of masked deoxynivalenol with Mn-doped CeO2 nanozyme as signal amplifier

Deoxynivalenol-3-glucoside (D3G), the masked form of the important mycotoxin deoxynivalenol (DON), displays potential toxicity but is difficult to control owing to the lack of rapid detection methods. Herein, an innovative molecularly imprinted polymer (MIP)-based electrochemical sensor was developed for the rapid detection of D3G. MIP, an efficient recognition element for D3G, was electropolymerized using o-phenylenediamine based on a surface functional monomer-directing strategy for the first time. CeO2, which contains both Ce3+ and Ce4+ oxidation states, was introduced as a nanozyme to catalyze H2O2 reduction, while Mn doping generated more oxygen vacancies and considerably improved the catalytic activity. Mn-CeO2 also served as a promising substrate material because of its large surface area and excellent conductivity. Under optimal conditions, a good linear relationship was observed for D3G detection over the concentration range of 0.01-50 ng/mL. The proposed sensor could detect D3G down to 0.003 ng/mL with excellent selectivity, even distinguishing its precursor DON in complex samples. The sensor exhibited acceptable stability with high reproducibility and accuracy, and could successfully determine D3G in grain samples. To the best of our knowledge, this is the first electrochemical sensing platform for rapid D3G detection that can easily be expanded to other masked mycotoxins.

Impact of morphology and oxygen vacancy content in Ni, Fe co-doped ceria for efficient electrocatalyst based water splitting

Designing a highly efficient, low-cost, sustainable electrocatalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) through water splitting is a current challenge for renewable energy technologies. This work presents a modified sol-gel route to prepare metal-ion(s) doped cerium oxide nanostructures as an efficient electrocatalyst for overall water splitting. Nickle (Ni) and iron (Fe) co-doping impacts the morphology in cerium oxide resulting in 5 nm nanoparticles with a mesoporous-like microstructure. The high level 20 mol% (1 : 1 ratio) of Ni + Fe bimetal-ion(s) doped CeO2 shows excellent HER and OER activities compared to the monodoped Fe/Ni and pristine CeO2. The co-doped catalysts required a low overpotential of 104 mV and 380 mV for HER and OER, respectively, in 1 M KOH, at a current density of 10 mA cm-2. The Tafel slopes of 95 mV dec-1 and 65 mV dec-1 were measured for HER and OER with the same representative samples which demonstrated excellent stability even after continuous operation for 20 hours in the alkaline medium. The unique morphology, enhanced oxygen vacancy (Ov) content and the synergistic effects of dopants in CeO2 play essential roles in enhancing the activities of Ni + Fe doped samples.

Electrochemiluminescence quenching effect of Cu2O towards flower-like ferric ion-doped g-C3N4 and its application for Cyfra21-1 immunosensing

In this article, ferric ion-doped floral graphite carbon nitride (Fe-CN-3, energy donor) was used to construct the substrate of the immunosensor and copper oxide nanocubes (Cu2O, energy acceptor) were taken as an efficient ECL quenching probe. A sandwich quench electrochemiluminescence (ECL) immunosensor for soluble cytokeratin 19 fragment (Cyfra21-1) detection was preliminarily developed based on a novel resonant energy transfer donor-acceptor pair. Fe-CN-3, a carbon nitride that combines the advantages of metal ion doping as well as morphology modulation, is used in ECL luminophores to provide more excellent ECL performance, which makes a significant contribution to the application and development of carbon nitride in the field of ECL biosensors. The regular shape, high specific surface area and excellent biocompatibility of the quencher Cu2O nanocubes facilitate the labeling of secondary antibodies and the construction of sensors. Meanwhile, as an energy acceptor, the UV absorption spectrum of Cu2O can overlap efficiently with the energy donor's ECL emission spectrum, making it prone to the occurrence of ECL-RET and thus obtaining an excellent quenching effect. These merits of the donor-acceptor pair enable the sensor to have a wide detection range of 0.00005-100 ng/mL and a low detection limit of 17.4 fg/mL (S/N = 3), which provides a new approach and theoretical basis for the clinical detection of lung cancer.

High performance photoelectrochemical immunosensing platform based on front-illuminated Mo:BiVO4 photoelectrodes for procalcitonin assay

The outstanding photoactive materials are the imperative for the construction of a front-illuminated photoelectrochemical (PEC) biosensor, which is crucial step for improving the detection sensitivity. Yet, the weak and unstable initial PEC signals of the photoelectrodes have limited evidently the detection performance. Herein, a front-illuminated "on-off" PEC immunosensor was constructed based on Mo:BiVO4 as photoactive matrix and Au/CeO2 as signal quencher for sensitive detection of procalcitonin (PCT). Systematic studies reveal that the Mo doped BiVO4 can increase the charge carrier density of BiVO4, leading to much higher initial signal under front illumination than back illumination. Moreover, Mo:BiVO4 was directly grown on conducting substrates, which effectively overcomes the loose combination of sensing substrate ensuring good electrical contact and continuity. Upon coupling with Au/CeO2 as signal quencher, the initial photocurrent signal can be significantly quenched. As a result, the proposed PEC immunosensor presents a wide linear range from 10 fg mL-1 to 50 ng mL-1 with a detection limit of 2.45 fg mL-1. Impressively, this study will open a new avenue for the construction of highly efficient and stable photoelectrode, as well as extend the application of PEC biosensor for biomarkers detection in early disease diagnosis.

Rapid Electrochemical Detection of Bacterial Sepsis in Cirrhotic Patients: A Microscaffold-Based Approach for Early Intervention

Sepsis is a dysregulated inflammatory response leading to multiple organ failure. Current methods of sepsis detection are time-consuming, involving nonspecific clinical signs, biomarkers, and blood cultures. Hence, efficient and rapid sepsis detection platforms are of utmost need for immediate antibiotic treatment. In the current study, a noninvasive rapid monitoring electrochemical sensing (ECS) platform was developed for the detection and classification of plasma samples of patients with liver cirrhosis by measuring the current peak shifts using the cyclic voltammetry (CV) technique. A total of 61 hospitalized cirrhotic patients with confirmed (culture-positive) or suspected (culture-negative) sepsis were enrolled. The presence of bacteria in the plasma was observed by growth kinetics, and for rapidness, the samples were co-encapsulated in microscaffolds with carbon nanodots that were sensitive enough to detect redox changes occurring due to the change in the pH of the surrounding medium, causing shifts in current peaks in the voltammograms within 2 h. The percentage area under the curve for confirmed infections was 94 and that with suspected cases was 87 in comparison to 69 and 71 with PCT, respectively. Furthermore, the charge was measured for class identification. The charge for LPS-absent bacteria ranged from -400 to -600 μC, whereas the charge for LPS-containing bacteria class ranged from -290 to -300 μC. Thus, the developed cost-effective system was sensitive enough to detect and identify bacterial sepsis.

Simple and sensitive sandwich-like voltammetric immunosensing of procalcitonin

Procalcitonin (PCT) is a reliable biomarker in the early diagnosis of septicemia, pyemia and stroke-associated pneumonia. In this work, through preparing β-cyclodextrin/graphene (CD/GN) nanohybrid as carrier and amplifier simultaneously to band antibodies and probe molecules, a simple and innovative sandwich-like voltammetric immunosensor was proposed for the sensitive and effective determination of PCT. Owing to the host-guest recognition property, the antibodies of PCT can enter into the CD cavities to generate a stable complex; meanwhile, aminopyrene (AP) were introduced as the signal probe and it was adsorbed on the surface of GN via aminopyrine π-πinteraction. Based on the signal change from AP as a response signal which exhibits linearity to the concentration of PCT, a highly sensitive sandwich-type voltammetric immunosensor was developed successfully after optimizing various key parameters. The results demonstrated that the developed sensor had a considerably low detection limit (0.003 pg mL-1) and wide linearity of 0.01 pg mL-1 to 20.0 ng mL-1. This work offered a very simple and sensitive sensing strategy for PCT and other biomarkers via altering the specific antibodies simply, showing great potential applications.

Sensitive sensing of Hg(II) based on lattice B and surface F co-doped CeO2: Synergies of catalysis and adsorption brought by doping site engineering

Transition metal oxides are widely used in the detection of heavy metal ions (HMIs), and the co-doping strategy that introducing a variety of different dopant atoms to modify them can obtain a better detection performance. However, there is very little research on the co-doped transition metal oxides by non-metallic elements for electrochemical detection. Herein, boron (B) and fluorine (F) co-doped CeO2 nanomaterial (BFC) is constructed to serve as the electrochemically sensitive interface for the detection of Hg(II). B and F affect the sensitivity of CeO2 to HMIs when they were introduced at different doping sites. Through a variety of characterization, it is proved that B is successfully doped into the lattice and F is doped on the surface of the material. Through the improvement of the catalytic properties and adsorption capacity of CeO2 by different doping sites, this B and F co-doped CeO2 exhibits excellent square wave anodic stripping voltammetry (SWASV) current responses to Hg(II). Both the high sensitivity of 906.99 μA μM-1 cm-2 and the low limit of detection (LOD) of 0.006 μM are satisfactory. Besides, this BFC glassy carbon electrode (GCE) also has good anti-interference property, which has been successfully used in the detection of Hg(II) in actual water. This discovery provides a useful strategy for designing a variety of non-metallic co-doped transition metal oxides to construct trace heavy metal ion-sensitive interfaces.

A micro-chamber free digital bio-detection for multiplexed and ultrasensitive immunoassay based on encoded magnetic microbeads and tyramide signal amplification strategy

Digital bio-detection has become one of the most appealing methods in recent years due to its excellent performance with ultra-sensitivity in detection of low-abundance targets. Traditional digital bio-detection needs the utilization of micro-chambers for physical isolation of targets, while the recently developed beads-based micro-chamber free one is attracting extensive attention, although there exist the disadvantages of overlaps between positive ("1") and negative ("0") signals as well as the decreased detection sensitivity in multiplexed mode. Here we propose a feasible and robust micro-chamber free digital bio-detection for multiplexed and ultrasensitive immunoassay based on encoded magnetic microbeads (EMMs) and tyramide signal amplification (TSA) strategy. An EMMs-based multiplexed platform is constructed by using a fluorescent encoding method, then a puissant signal amplification of positive events in TSA procedure is achieved via systematical revelation of key factors influences. For proof of concept, a three-plexed tumor markers detection is performed to evaluate our established platform. The detection sensitivity is comparable to the corresponding single-plexed assays and is also approximately 30-15,000 times improvement compared to the conventional suspension chip. Therefore, this multiplexed micro-chamber free digital bio-detection paves a promising way to be an ultrasensitive and powerful tool for clinical diagnosis.

Hollow SnO2/CdS QDs/CdCO3 heterostructured nanocubes coupled with hollow PtPd/MnCo-CeO2 nanozyme-mediated synergistic amplification for ultrasensitive PEC immunoanalysis of lung cancer biomarker

Nowadays, lung cancer is one of the most dangerous cancers threatening human life all over the world. As a crucial biomarker, cytokeratin 19 fragment 21-1 (CYFRA 21-1) is extraordinary important for diagnosis of non-small cell lung cancer (NSCLC). In this work, we synthesized hollow SnO₂/CdS QDs/CdCO₃ heterostructured nanocubes with high and stable photocurrents, which applied to construction of a sandwich-typed photoelectrochemical (PEC) immunosensor for detection of CYFRA 21-1, integrated by in-situ catalytic precipitation strategy with home-built PtPd alloy anchored MnCo-CeO₂ (PtPd/MnCo-CeO₂) nanozyme for synergistic amplification. The interfacial electron transfer mechanism upon visible-light irradiation was investigated in details. Further, the PEC responses were seriously quenched by the specific immunoreaction and precipitation catalyzed by the PtPd/MnCo-CeO₂ nanozyme. The established biosensor showed a wider linear range of 0.001-200 ng mL^-1 and a lower limit of detection (LOD = 0.2 pg mL^-1, S/N = 3), coupled by exploring such analysis even in diluted human serum sample. This work opens a constructive avenue to develop ultrasensitive PEC sensing platforms for detecting diverse cancer biomarkers in clinic.

Bimetallic AuPt alloy/rod-like CeO2 nanojunctions with high peroxidase-like activity for colorimetric sensing of organophosphorus pesticides

Organophosphorus pesticides (OP) have extensive applications in agriculture, while their overuse causes inevitable residues in food, soil, and water, ultimately being harmful to human health and even causing diverse dysfunctions. Herein, a novel colorimetric platform was established for quantitative determination of malathion based on peroxidase mimic AuPt alloy decorated on CeO₂ nanorods (CeO₂@AuPt NRs). The synthesized nanozyme oxidized colorless 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂. Besides, the oxidized TMB was inversely reduced by ascorbic acid (AA), which were originated from hydrolysis of L-ascorbic acid-2-phosphate (AA2P) with the assistance of acid phosphatase (ACP). Based upon this observation ACP analysis was explored by colorimetry, showing a wid linear range of 0.2 ~ 3.5 U L^-1 and a low limit of detection (LOD = 0.085 U L^-1, S/N = 3). Furthermore, malathion present in the colorimetric system inhibited the activity of ACP and simultaneously affected the generation of AA, in turn promoting the recovery of the chromogenic reaction. Based on this, the LOD was decreased to 1.5 nM (S/N = 3) for the assay of malathion with a wide linear range of 6 ~ 100 nM. This simple colorimetric platform provides some informative guidelines for determination of other pesticides and disease markers.

Dual-mode biosensor platform based on synergistic effects of dual-functional hybrid nanomaterials

Detection of biomarkers is very vital in the prevention, diagnosis and treatment of diseases. However, due to the poor accuracy and sensitivity of the constructed biosensors, we are now facing great challenges. In addressing these problems, nanohybrid-based dual mode biosensors including optical-optical, optical-electrochemical and electrochemical-electrochemical have been developed to detect various biomarkers. Integrating the merits of nanomaterials with abundant active sites, synergy and excellent physicochemical properties, many bi-functional nanohybrids have been reasonable designed and controllable preparation, which applied to the construction dual mode biosensors. Despite the significant progress, further efforts are still needed to develop dual mode biosensors and ensure their practical application by using portable digital devices. Therefore, the present review summarizes an in-depth evaluation of the bi-functional nanohybrids assisted dual mode biosensing platform of biomarkers. We are hoping this review could inspire further concepts in developing novel dual mode biosensors for possible detection application.

Recent Progress in Nanotechnology-Based Approaches for Food Monitoring

Throughout the food supply chain, including production, storage, and distribution, food can be contaminated by harmful chemicals and microorganisms, resulting in a severe threat to human health. In recent years, the rapid advancement and development of nanotechnology proposed revolutionary solutions to solve several problems in scientific and industrial areas, including food monitoring. Nanotechnology can be incorporated into chemical and biological sensors to improve analytical performance, such as response time, sensitivity, selectivity, reliability, and accuracy. Based on the characteristics of the contaminants and the detection methods, nanotechnology can be applied in different ways in order to improve conventional techniques. Nanomaterials such as nanoparticles, nanorods, nanosheets, nanocomposites, nanotubes, and nanowires provide various functions for the immobilization and labeling of contaminants in electrochemical and optical detection. This review summarizes the recent advances in nanotechnology for detecting chemical and biological contaminations in the food supply chain.

Ultrasensitive sandwich-typed electrochemical immunoassay for detection of squamous cell carcinoma antigen based on highly branched PtCo nanocrystals and dendritic mesoporous SiO2@AuPt nanoparticles

Squamous cell carcinoma antigen (SCCA) is one of the common squamous cell carcinomas (SCC) in women, which usually works as a tumor biomarker for cervical cancer in diagnostic applications. Herein, bimetallic PtCo highly branched nanocrystals (PtCo BNCs) acted as electrode substrates to construct sandwich-typed electrochemical immunosensor for ultrasensitive detection of SCCA, by using dendritic mesoporous SiO₂@AuPt nanoparticles (DM-SiO₂@AuPt NPs) to adsorb electroactive thionine (Thi) as a signal label. The PtCo BNCs enlarged the loading of the primary antibody (Ab₁), showing effective improvement in conductivity and sensitivity. The DM-SiO₂ had abundant pores to incorporate more Thi, on which the decorated AuPt NPs created a great number of active sites to immobilize the secondary antibodies (Ab₂), thereby obviously amplifying the detection signals. The prepared sensor exhibited a broader linear range (0.001-120 ng mL^-1) and a lower detection limit (0.33 pg mL^-1, S/N = 3), combined with high reproducibility, a low relative standard deviation (below 2.5%) and acceptable recovery (from 98.5 to 110.0%) even in diluted human serum samples. This research provides a substantial platform for clinical diagnosis of SCCA in practice.

The role of doping strategy in nanoparticle-based electrochemiluminescence biosensing

Doping plays a crucial role in electrochemiluminescence (ECL) due to the followings: (1) Modulation of electronic structure, alteration of the surface state of nanoparticles (NPs), providing effective protection from the surrounding environment, thereby leading to ECL emitters with exceptional properties including tunable spectra, high luminescence efficiency, low excitation potential, and good stability. (2) Employment of doped NPs as promising coreactant alternatives due to the presence of functional groups such as amines induced by NP doping. (3) Serving as novel co-reaction accelerators (CRAs) for ECL through doping induced high catalytic properties. (4) Behaving as excellent carriers to load ECL emitters, recognition elements, and catalysts due to doping-induced larger surface area, higher conductivity and better biocompatibility of NPs. As a consequence, doped NPs have aroused broad interest and found wide applications in various ECL sensing platforms. In this review, the current promising improvements, concepts, and excellent applications of doped NPs for ECL biosensing are addressed. We aim to bring to light the physicochemical characteristics of various doped NPs that endow them with appealing ECL performance, leading to diverse applications in biosensing.

A sandwich-type electrochemical immunosensor for CYFRA 21-1 based on probe-confined in PtPd/polydopamine/hollow carbon spheres coupled with dendritic Au@Rh nanocrystals

A signal-on sandwich-like electrochemical immunosensor was built for determination of cytokeratin 19 fragments 21-1 (CYFRA 21-1) in non-small cell lung cancer (NSCLC) by confining electroactive dye (e.g., methylene blue, MB) as a probe for amplifying signals. Specifically, core-shell gold@rhodium dendritic nanocrystals (Au@Rh DNCs) behaved as a substrate for primary antibody and accelerate interfacial electron transfer. Besides, hollow carbon spheres (HCSs) were subsequently modified with polydopamine (PDA) and PtPd nanoparticles for sequential integration of the secondary antibody and confinement of MB as a label, termed as MB/PtPd/PDA/HCSs for clarity. The built sensors showed a broad linear range (100 fg mL^-1 ~ 100 ng mL^-1) for detection of CYFRA 21-1 with an ultra-low detection limit (31.72 fg mL^-1, S/N = 3), coupled with satisfactory performance in human serum samples. This work can be explored for assays of other proteins and provides some constructive insights for early and accurate diagnosis of NSCLC.

Advanced Metal-Organic Frameworks-Based Catalysts in Electrochemical Sensors

Developing efficient catalysts is vital for the application of electrochemical sensors. Metal-organic frameworks (MOFs), with high porosity, large specific surface area, good conductivity, and biocompatibility, have been widely used in catalysis, adsorption, separation, and energy storage applications. In this invited review, the recent advances of a novel MOF-based catalysts in electrochemical sensors are summarized. Based on the structure-activity-performance relationship of MOF-based catalysts, their mechanism as electrochemical sensor, including metal cations, synthetic ligands, and structure, are introduced. Then, the MOF-based composites are successively divided into metal-based, carbon-based, and other MOF-based composites. Furthermore, their application in environmental monitoring, food safety control, and clinical diagnosis is discussed. The perspective and challenges for advanced MOF-based composites are proposed at the end of this contribution.

MOF-derivated MnO@C nanocomposite with bidirectional electrocatalytic ability as signal amplification for dual-signal electrochemical sensing of cancer biomarker

Dual-signal strategy has great potential in improving the accuracy and sensitivity of cancer biomarker determination. However, most sensors based on nanomaterials as signal amplification usually output single detectable signal. It is still a challenge to achieve dual-signal sensing of biomarkers with nanomaterials as signal amplification. Herein, MnO@C nanocomposite was prepared with Mn-MOF-74 as precursor by pyrolysis. It possesses bidirectional electrocatalytic ability toward both oxidation and reduction of H₂O₂ for its fully exposed crystal facets. After loading AuNPs, MnO@C@AuNPs can connect aptamer (Apt) via Au-S and then as a signal amplification for the construction of sandwich-type aptasensor for dual-signal electrochemical sensing of cancer biomarker. Thus, taking mucin 1 (MUC1) as a model system. The aptasensor has the parallel output of differential pulse voltammetry (DPV) and chronoamperometry responses based on oxidation and reduction of H₂O₂, respectively, which implemented sensitive and accurate measurements to avoid false results. The linear response ranges of 0.001 nM-100 nM (detection limit of 0.31 pM) for DPV technique and 0.001 nM-10 nM (detection limit of 0.25 pM) for chronoamperometry technique were obtained. It opens up a new way to design elegant dual-signal aptasensors with potential applications in early disease diagnosis.

Nanoplatforms for Sepsis Management: Rapid Detection/Warning, Pathogen Elimination and Restoring Immune Homeostasis

Sepsis, a highly life-threatening organ dysfunction caused by uncontrollable immune responses to infection, is a leading contributor to mortality in intensive care units. Sepsis-related deaths have been reported to account for 19.7% of all global deaths. However, no effective and specific therapeutic for clinical sepsis management is available due to the complex pathogenesis. Concurrently eliminating infections and restoring immune homeostasis are regarded as the core strategies to manage sepsis. Sophisticated nanoplatforms guided by supramolecular and medicinal chemistry, targeting infection and/or imbalanced immune responses, have emerged as potent tools to combat sepsis by supporting more accurate diagnosis and precision treatment. Nanoplatforms can overcome the barriers faced by clinical strategies, including delayed diagnosis, drug resistance and incapacity to manage immune disorders. Here, we present a comprehensive review highlighting the pathogenetic characteristics of sepsis and future therapeutic concepts, summarizing the progress of these well-designed nanoplatforms in sepsis management and discussing the ongoing challenges and perspectives regarding future potential therapies. Based on these state-of-the-art studies, this review will advance multidisciplinary collaboration and drive clinical translation to remedy sepsis.

A DNA dendrimer amplified electrochemical immunosensing method for highly sensitive detection of prostate specific antigen

This work designed a DNA dendrimer for the loading of signal molecule and the construction of amplified electrochemical immunosensing method. The DNA dendrimer was self-assembled by the hybridization of one couple of complementary oligonucleotides (DNA and cDNA) that were covalently conjugated to three arms of a Y-shaped cross-linker, tris(2-maleimidoethyl)amine (TMEA) respectively. The immunosensor was prepared by coating chitosan on glassy carbon electrode to covalently immobilize the capture antibody with glutaraldehyde as a linker. After the target protein was captured on the immunosensor, cDNA-labeled secondary antibody was bound on the surface via a sandwiched immunoreaction to introduce the DNA dendrimer onto immunosensor for loading abundant methylene blue as signal molecule, which amplified greatly the amperometric signal for immunoassay. Using prostate specific antigen (PSA) as a model analyte, this proposed method showed a wide linear range from 1 pg mL^-1 to 10 ng mL^-1 along with a limit of detection down to 0.26 pg mL^-1. The designed strategy avoided complex synthesis of signal tags, and possessed excellent performance for analysis of practical samples, thus providing a new avenue for the development of signal amplification strategy and immunoassay methods.

Nanoceria, the versatile nanoparticles: Promising biomedical applications

Nanotechnology has been a boon for the biomedical field due to the freedom it provides for tailoring of pharmacokinetic properties of different drug molecules. Nanomedicine is the medical application of nanotechnology for the diagnosis, treatment and/or management of the diseases. Cerium oxide nanoparticles (CNPs) are metal oxide-based nanoparticles (NPs) which possess outstanding reactive oxygen species (ROS) scavenging activities primarily due to the availability of "oxidation switch" on their surface. These NP have been found to protect from a number of disorders with a background of oxidative stress such as cancer, diabetes etc. In fact, the CNPs have been found to possess the environment-dependent ROS modulating properties. In addition, the inherent catalase, SOD, oxidase, peroxidase and phosphatase mimetic properties of CNPs provide them superiority over a number of NPs. Further, chemical reactivity of CNPs seems to be a function of their surface chemistry which can be precisely tuned by defect engineering. However, the contradictory reports make it necessary to critically evaluate the potential of CNPs, in the light of available literature. The review is aimed at probing the feasibility of CNPs to push towards the clinical studies. Further, we have also covered and censoriously discussed the suspected negative impacts of CNPs before making our way to a consensus. This review aims to be a comprehensive, authoritative, critical, and accessible review of general interest to the scientific community.

Enhanced Catalytic Activity Induced by the Nanostructuring Effect in Pd Decoration onto Doped Ceria Enabling an Origami Paper Analytical Device for High Performance of Amyloid-β Bioassay

In this work, we fabricated a novel origami paper-based analytical device (oPAD) assisted by the nanostructuring effect of in situ Pd decoration of Cu/Co-doped CeO₂ (CuCo-CeO₂-Pd) nanospheres, functionalized with their strongly enhanced electrocatalytic properties to realize an electrochemical and visual signal readout system in oPAD, for highly sensitive detection of amyloid-β (Aβ). The CuCo-CeO₂-Pd nanospheres were introduced as an enhanced "signal transducer layer" on account of the electron transfer acceleration caused by catalyzing glucose to produce H₂O₂ for differential pulse voltammetry signal readout and further 3,3'5,5'-tetramethylbenzidine (TMB) oxidation for colorimetric analysis. Meanwhile, for achieving superior performance of the proposed oPAD, in situ growth of urchin-like gold nanoparticles (Au NPs) onto cellulose fibers was adopted to improve "the recognition layer" in favor of immobilizing antibodies for targeting Aβ through specific antigen-antibody interactions. Combined with the delicate design of oPAD, exhibiting actuation of the conversion procedure between hydrophobicity and hydrophilicity on paper tabs in the assay process, the oPAD successfully enabled sensitive diagnosis of Aβ in a linear range from 1.0 pM to 100 nM with a limit of detection of 0.05 pM (S/N = 3) for electrochemical detection, providing a reliable strategy for quantifying the Aβ protein in clinical applications.

Electrochemical Immunosensors for Quantification of Procalcitonin: Progress and Prospects

Human procalcitonin (PCT) is a peptide precursor of the calcium-regulating hormone calcitonin. Traditionally, PCT has been used as a biomarker for severe bacterial infections and sepsis. It has also been recently identified as a potential marker for COVID-19. Normally, serum PCT is intracellularly cleaved to calcitonin, which lowers the levels of PCT (<0.01 ng/mL). In severe infectious diseases and sepsis, serum PCT levels increase above 100 ng/mL in response to pro-inflammatory stimulation. Development of sensors for specific quantification of PCT has resulted in considerable improvement in the sensitivity, linear range and rapid response. Among the various sensing strategies, electrochemical platforms have been extensively investigated owing to their cost-effectiveness, ease of fabrication and portability. Sandwich-type electrochemical immunoassays based on the specific antigen–antibody interactions with an electrochemical transducer and use of nanointerfaces has augmented the electrochemical response of the sensors towards PCT. Identification of a superior combination of electrode material and nanointerface, and translation of the sensing platform into flexible and disposable substrates are under active investigation towards development of a point-of-care device for PCT detection. This review provides an overview of the existing detection strategies and limitations of PCT electrochemical immunosensors, and the emerging directions to address these lacunae.

Neonatal sepsis at point of care

Sepsis, which includes infection followed by inflammation, is one of the leading causes of death among neonates worldwide. The major attribute of this disease process is dysregulated host response to infection leading to organ dysfunction and potentially death. A comprehensive understanding of the host response as well as the pathogen itself are important factors contributing to outcome. Early diagnosis is paramount, as it leads to accurate assessment and improved clinical management. Accordingly, a number of diagnostic platforms have been introduced to assess the presence of blood stream pathogens in septic neonates. Unfortunately, current point-of-care (POC) methods rely on a single parameter/biomarker and thus lack a comprehensive evaluation. The emerging field of biosensing has, however, resulted in the development of a wide range of analytical devices that may be useful at POC. This review discusses currently available methods to screen the inflammatory process in neonatal sepsis. We describe POC sensor-based methods for single platform multi-analyte detection and highlight the latest advances in this evolving technology. Finally, we critically evaluate the applicability of these POC devices clinically for early diagnosis of sepsis in neonates.

Cost-effective paper-based electrochemical immunosensor using a label-free assay for sensitive detection of ferritin

Ferritin, a blood cell protein containing iron, is a crucial biomarker that is used to estimate the risk assessment of iron deficiency anemia. For point-of-care analysis, a reliable, cost-effective, selective, sensitive, and portable tool is extremely necessary. In this study, a label-free electrochemical immunosensor for detecting ferritin using a paper-based analytical device (ePAD) was created. The device pattern was custom designed onto filter paper to successfully fabricate a deliverable immunosensor. Graphene oxide was first modified onto the working electrode using an inkjet printing technique. An activation step of the electrode surface was then performed using standard 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysulfosuccinimide (sulfo-NHS) chemistry. Anti-ferritin antibodies were covalently immobilized onto the amine-reactive ester surface. The amount of ferritin was monitored by observing the electrochemical signal of the selected redox couple by differential pulse voltammetry (DPV). In the presence of ferritin, the sensor showed a considerable decrease in electrochemical response in a concentration-dependent manner. In contrast, there was no observable change in current response detected in the absence of ferritin. The current response provided a good correlation with ferritin concentrations in the range of 1 to 1000 ng mL-1, and the limit of detection (3SD/slope) was found to be 0.19 ng mL-1. This fabricated immunosensor offered good selectivity, reproducibility, and long-term storage stability. In addition, this proposed immunosensor was successfully applied to detect ferritin in human serum with satisfactory results. The promising results suggested that this handmade paper-based immunosensor may be an alternative device for the diagnosis of iron deficiency anemia.

An on-chip microfluidic-based electrochemical magneto-immunoassay for the determination of procalcitonin in plasma obtained from sepsis diagnosed preterm neonates

A novel on-chip electrochemical magneto-immunoassay for the determination of procalcitonin (PCT) has been proposed. The strategy involved the on-line performing of the biorecognition event and detection on the thin-film microfluidic gold electrode chamber operating at E = -0.20 V (vs. Au). The complete assay was performed in less than 15 minutes using only 25 μL of the sample, covering the entire range of clinically relevant PCT concentrations in sepsis diagnosis with a limit of detection and quantification of 0.02 ng mL-1 and 0.05 ng mL-1, respectively (the sepsis diagnosis threshold: 0.5 ng mL-1). The on-chip electrochemical magneto-immunoassay provided excellent results in the analysis of very unique samples obtained from preterm neonates admitted with suspected sepsis, in which the sample volume is hardly available. These characteristics fulfill the POCT requirements for PCT determination in the whole clinically relevant concentration range. Because of the high clinical relevance and the important role of PCT in sepsis, this approach opens new perspectives for sepsis diagnosis and therapy guidance using low volume samples.

Catalytic hairpin assembly-based electrochemical biosensor with tandem signal amplification for sensitive microRNA assay

We demonstrate for the first time the construction of a low background electrochemical biosensor with tandem signal amplification for sensitive microRNA assay based on target-activated catalytic hairpin assembly (CHA) of heteroduplex-templated copper nanoparticles. This electrochemical biosensor exhibits high sensitivity, good specificity, single-base mismatch discrimination capability, excellent stability and reproducibility, and it can sensitively detect microRNA in cancer cells.

Fenton reaction-mediated dual-attenuation of signal for ultrasensitive amperometric immunoassay

In order to alter the complexion of immunoprobe with large impedance as negative factor in sensitivity of amperometric immunosensor, a strategy of Fenton reaction-mediated dual-attenuation of signal was proposed. Herein, metal-polydopamine-Fe³⁺ composite with the ability of Fenton reaction was initially prepared as immunoprobe for an ultrasensitive immunoassay. The polymerization of dopamine occurred on the surface of ZIF-67 to gain the metal-polydopamine shell, which possessed rich functional groups, negative charge and high specific surface. Then the prepared functional shell was further used to absorb Fe³⁺ and immobilize labeling antibody as immunoprobe, which was used to construct a sandwich type immunosensor. With addition of H₂O₂ and aniline, Fenton reaction was triggered to produce hydroxyl radicals, which can not only decrease the current value by degrading methylene blue molecules, but also further initiate aniline to polymerize into non-conductive polyaniline for successive abatement of signal intensity. Therefore, the dual-attenuation of signal model rendered the immunoprobe into a favorable factor and synchronously enhance sensitivity. Expectedly, the detection performance with a linear range from 1.0 × 10^-4-100 ng mL^-1 and ultralow detection limit of 9.07 × 10^-5 ng mL^-1 toward neuron-specific enolase was obtained under optimal conditions. This work offered a novel tactic for enhancing sensitivity of immunosensor through the preparation of functional immunoprobe and its rational utilization as signal enhancer.

Metal composite oxides Bi2MoO6/IL membrane as matrix for constructing ultrasensitive electrochemical immunosensor

In the process of diagnosis and disease monitoring, it is important to quickly and easily detect protein biomarkers. The strategy reported here is an attempt to prepare Bi₂MoO₆ nanomaterial with new three-dimensional holes morphology surrounded by rod and sheet to construct a simple and sensitive sensing platform, where Bi₂MoO₆/ionic liquid (IL) composite was modified on the carbon paste electrode (CPE). In order to monitor the assembly process of human IgG immunosensors, a plurality of electrochemical tests such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) was executed. The obtained BSA/anti-IgG/GA/Bi₂MoO6/IL-CPE displayed prominent conductivity and high sensitivity in detecting human immunoglobulin G (human IgG). Under the optimal experimental conditions, the results by differential pulse voltammetry (DPV) showed that the constructed label-free IgG immunosensor can detect IgG in the range of 0.01 to 1000 ng mL^-1, and limit of detection (LOD) was 4 pg mL^-1. The immunosensor displayed good performances including selectivity, reproducibility, and stability. Based on preliminary experiments, Bi₂MoO₆ and its composite materials are very promising for the construction of a variety biosensors for the analysis of other biological substances. Graphical abstract.

Impact of nanoceria shape on degradation of diethyl paraoxon: Synthesis, catalytic mechanism, and water remediation application

A series of nanomaterials have been demonstrated to be powerful for direct degradation of diethyl paraoxon (EP) to diethyl phosphate and 4-nitrophenol in aqueous solution. However, comparison of catalytic activity of different nanomaterials toward EP is rarely explored. In the present study, four different morphological nanoceria (cubes, rods, polyhedral, and spheres) were synthesized, characterized, and evaluated as a catalyst for the degradation of EP in comparison to other commercially available nanomaterials. Among the tested nanoceria, the cerium dioxide (CeO₂) nanopolyhedra possess the best catalytic activity toward the hydrolysis of EP owing to their abundant oxygen vacancy sites, optimal ratio of Ce(III) to Ce(IV), and specific exposed facets. Under the conditions of 0.2 M NH₃/NH₄Cl buffer and 25 °C, the CeO₂ nanopolyhedra catalyzed the reduction of EP to 4-nitrophenol with a >99% conversion at pH 8.0 for 50 h, at pH 10.0 for 12 h, and at pH 12.0 for 2.5 h. The catalytic degradation of nearly 100% EP in NH₃/NH₄Cl buffer (pH 10.0) at 25 °C is in the decreasing order of CeO₂ nanopolyhedra > CeO₂ nanorods > ZnO nanospheres (NSs) > CeO₂ nanocubes > TiO₂ NSs > CeO₂ NSs > Fe₃O₄ NSs ~ Co₃O₄ NSs ~ control experiment. The mechanism for the degradation of EP was confirmed by monitoring catalytic kinetics of the CeO₂ nanopolyhedra in the presence of EP, dimethyl paraoxon, 4-nitrophenyl phosphate, and parathion. The nanocomposites were simply fabricated by electrostatic self-assembly of the CeO₂ nanopolyhedra and poly(diallyldimethylammonium chloride)-capped gold nanoparticles (PDDA-AuNPs). The resultant nanocomposites still efficiently catalyzed NaBH₄-mediated reduction of 4-nitrophenol to 4-aminophenol with a normalized rate constant of 6.68 ± 0.72 s^-1 g^-1 and a chemoselectivity of >99%. In confirmation of the robustness and applicability of the as-prepared nanocomposites, they were further used to catalyze the degradation of EP to 4-amionphenol in river water and seawater.

Recent advances in developing biosensing based platforms for neonatal sepsis

Neonatal sepsis is a bloodstream infection primarily caused by Escherichia coli (E. coli), Group B Streptococcus (GBS), Listeria monocytogenes, Haemophilus influenzae, S. aureus, Klebsiella spp. and non-typhoidal Salmonella bacteria. Neonatal Sepsis is referred as a critical response to the infection in the neonatal period that can lead to the failure of body organs and thereby causing damage to the tissues resulting in death of the neonates. Nearly 4 million deaths across the world are occurred due to neonatal sepsis infections. In order to prevent the bloodstream infections in the neonates, it is indispensable to diagnose the disease properly for appropriate treatment during the point of care. Numerous studies have been reported to identify major biomarkers associated with neonatal sepsis including Serum Amyloid A (SAA), C - reactive protein (CRP), Procalcitonin (PCT) and Lipopolysaccharide-binding protein (LBP). Distinct diagnostic platforms have also been developed detecting the presence of bloodstream infections including electrochemical, potentiometric, and impedimetric sensors. Recently, electrochemical biosensors with the integration of nanomaterials have emerged as a better platform for neonatal sepsis biomarkers detection. This review article summarizes the diverse screening platforms, evaluation parameters, and new advances based on implications of nanomaterials for the development of biosensors detecting neonatal sepsis infections. The review further elucidates the significance and future scope of distinctive platforms which are predominantly associated with detection of neonatal sepsis.

Nanobioconjugates for Signal Amplification in Electrochemical Biosensing

Nanobioconjugates are hybrid materials that result from the coalescence of biomolecules and nanomaterials. They have emerged as a strategy to amplify the signal response in the biosensor field with the potential to enhance the sensitivity and detection limits of analytical assays. This critical review collects a myriad of strategies for the development of nanobioconjugates based on the conjugation of proteins, antibodies, carbohydrates, and DNA/RNA with noble metals, quantum dots, carbon- and magnetic-based nanomaterials, polymers, and complexes. It first discusses nanobioconjugates assembly and characterization to focus on the strategies to amplify a biorecognition event in biosensing, including molecular-, enzymatic-, and electroactive complex-based approaches. It provides some examples, current challenges, and future perspectives of nanobioconjugates for the amplification of signals in electrochemical biosensing.

Magnetic Bead-Based Electrochemical Immunoassays On-Drop and On-Chip for Procalcitonin Determination: Disposable Tools for Clinical Sepsis Diagnosis

Procalcitonin (PCT) is a known protein biomarker clinically used for the early stages of sepsis diagnosis and therapy guidance. For its reliable determination, sandwich format magnetic bead-based immunoassays with two different electrochemical detection approaches are described: (i) disposable screen-printed carbon electrodes (SPE-C, on-drop detection); (ii) electro-kinetically driven microfluidic chips with integrated Au electrodes (EMC-Au, on-chip detection). Both approaches exhibited enough sensitivity (limit of detection (LOD) of 0.1 and 0.04 ng mL⁻¹ for SPE-C and EMC-Au, respectively; cutoff 0.5 ng mL⁻¹), an adequate working range for the clinically relevant concentrations (0.5–1000 and 0.1–20 ng mL⁻¹ for SPE-C and EMC-Au, respectively), and good precision (RSD < 9%), using low sample volumes (25 µL) with total assay times less than 20 min. The suitability of both approaches was successfully demonstrated by the analysis of human serum and plasma samples, for which good recoveries were obtained (89–120%). Furthermore, the EMC-Au approach enabled the easy automation of the process, constituting a reliable alternative diagnostic tool for on-site/bed-site clinical analysis.

Polymer-Based Micromotor Fluorescence Immunoassay for On-the-Move Sensitive Procalcitonin Determination in Very Low Birth Weight Infants' Plasma

A new fluorescence micromotor-based immunoassay (FMIm) has been developed for procalcitonin (PCT) determination as an early sepsis diagnostic analytical tool. The micromotors combine the high binding capacity of the specific antibodies onto their polymeric polypyrrole outer layer (PPy layer), with their magnetic guidance (Ni layer) and self-propulsion by catalytic generation of oxygen bubbles (PtNP inner layer) to actively recognize the PCT antigen. This FMIm allowed a sensitive (LOD = 0.07 ng mL^-1) and direct PCT determination in clinical samples from very low-birth-weight infants (VLBWI) with sepsis suspicion, using small volumes of sample (25 μL) in a clinically relevant range of concentrations (0.5-150 ng mL^-1). The good agreement between PCT levels obtained by our micromotor-based method and routine immunofluorescence hospital determination demonstrates the feasibility for the analysis in VLBWI samples and its potential as a point-of-care diagnostic tool for sepsis.

Facile Synthesis of Eggshell Membrane-Templated Au/CeO2 3D Nanocomposite Networks for Nonenzymatic Electrochemical Dopamine Sensor

Dopamine acts as a neurotransmitter to regulate a variety of physiological functions of the central nervous system. Thus, the fabrication of electrochemical active nanomaterials for sensitive dopamine detection is extremely important for human health. Herein, we constructed a highly efficient dopamine nonenzymatic biosensor using eggshell membrane (ESM) as a 3D network-like carrier-loaded Au and CeO₂ nanocomposites. This approach has led to the uniform distribution of CeO₂ and Au nanoparticles on the surface of ESM. The structure and properties of the as-prepared ESM templated Au/CeO₂ (ESM-AC) nanocomposites were characterized. The electrochemical properties of non-enzymatic oxidation of dopamine by ESM-AC electrode were studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The detection limit of the ESM-AC modified electrode for dopamine is 0.26 μM with a linear range from 0.1 to 10 mM. The ESM-AC-modified electrode performs a higher catalytic activity for dopamine electrocatalytic oxidation than that ESM-templated CeO₂ (ESM-C) electrode, which is mainly due to the unique structure of ESM and more active sites provided from Au. Collectively, this biological waste-ESM provides a cheap and unique template for the preparation of 3D network-like nanostructures and expands the application in electrochemical dopamine detection. ESM-AC nanocomposites prepared from biological waste was successfully modified on the surface of glassy carbon electrode and a dopamine-based electrochemical biosensor was constructed.

Tailoring the CeO2 morphology and its electrochemical reactivity for highly sensitive and selective determination of dopamine and epinephrine

Four CeO₂ nanomaterials with the morphologies of a nanoplate (CeO₂-p), a nanocube (CeO₂-c), a porous triangular microplate (CeO₂-t), and of a porous hierarchical rod-stacked nanobundle (CeO₂-b) were synthesized using a hydrothermal method. They were characterized by scanning and transmission electron microscopies, X-ray diffraction and X-ray photoelectron spectroscopy. Electrochemical characterizations reveal the tuning of their morphology and the presence of exposed crystal planes of CeO₂ that can be realized by changing the alkali sources. Among these materials, the CeO₂-b features the largest specific surface and lowest electron transfer resistance towards the redox probe Fe(CN)₆^3-/4-. The best voltammetric response to dopamine and epinephrine is thus achieved by using the Nafion-CeO₂-b coated electrode. A sensitive and selective method was developed that can voltammetrically detect dopamine (with a peak near 0.13 V vs. SCE), and epinephrine (with a peak near 0.25 V vs. SCE). The detection limits are 2.9 and 0.67 nM, respectively. Graphical abstractSchematic representation of morphology tailoring of CeO₂ and electrochemical sensing of dopamine and epinephrine on these CeO₂ samples with different morphologies.

Biosensors for detecting viral and bacterial infections using host biomarkers: a review

A schematic diagram showing multiple modes of biosensing platforms for the diagnosis of bacterial or viral infections.