Versatile electrochemical biosensor based on bi-enzyme cascade biocatalysis spatially regulated by DNA architecture

Dual-mode optical biosensor based on multi-functional DNA structures for detecting bioactive small molecules

Semiconducting polymer dots and hemin-functionalized DNA nanoflowers with excellent peroxidase-like activity and high fluorescent brightness are prepared for fluorescent/colorimetric dual-mode sensing of dopamine and glutathione as low as nM and μM, respectively. This biosensor is readily applied to the analysis of complicated biological samples with high selectivity and accuracy, which opens up promising prospects in clinical applications.

Enzyme Cascade Electrode Reactions with Nanomaterials and Their Applicability towards Biosensor and Biofuel Cells

Nanomaterials, including carbon nanotubes, graphene oxide, metal-organic frameworks, metal nanoparticles, and porous carbon, play a crucial role as efficient carriers to enhance enzyme activity through substrate channeling while improving enzyme stability and reusability. However, there are significant debates surrounding aspects such as enzyme orientation, enzyme loading, retention of enzyme activity, and immobilization techniques. Consequently, these subjects have become the focus of intensive research in the realm of multi-enzyme cascade reactions. Researchers have undertaken the challenge of creating functional in vitro multi-enzyme systems, drawing inspiration from natural multi-enzyme processes within living organisms. Substantial progress has been achieved in designing multi-step reactions that harness the synthetic capabilities of various enzymes, particularly in applications such as biomarker detection (e.g., biosensors) and the development of biofuel cells. This review provides an overview of recent developments in concurrent and sequential approaches involving two or more enzymes in sequence. It delves into the intricacies of multi-enzyme cascade reactions conducted on nanostructured electrodes, addressing both the challenges encountered and the innovative solutions devised in this field.

Amphiphilic Polymer Capped Perovskite Compositing with Nano Zr-MOF for Nanozyme-Involved Biomimetic Cascade Catalysis

CsPbX3 perovskite nanocrystal (NC) is considered as an excellent optical material and is widely applied in optoelectronics. However, its poor water stability impedes its study in enzyme-like activity, and further inhibits its application in biomimetic cascade catalysis. Herein, for the first time, the oxidase-like and ascorbate oxidase-like activities of an amphiphilic polymer capped CsPbX3 are demonstrated, and its catalytic mechanism is further explored. Furthermore, an all-nanozyme cascade system (multifunctional CsPbBr3 @Zr-metal organic framework (Zr-MOF) and Prussian blue as oxidase-like and peroxidase-like nanozyme) is constructed with a portable paper-based device for realizing the dual-mode (ratiometric fluorescence and colorimetric) detection of ascorbic acid in a point-of-care (POC) fashion. This is the first report on the utilization of all-inorganic CsPbX3 perovskite NC in biomimetic cascade catalysis, which opens a new avenue for POC clinical disease diagnosis.

A smart TESTER for reliable discrimination of cancer-derived small extracellular vesicles

Cancer-derived small extracellular vesicles (csEVs) are crucial liquid biopsy indicators that reflect the presence and progression of many malignancies. However, reliable discrimination of csEVs remains a great challenge owing to the interference from normal sEVs (nsEVs) and low abundance in the early stages of cancer. In this work, we developed a Two-Elements Selectively Triggered csEVs Recognization (TESTER) strategy for selective identification of csEVs from the complex clinical body fluid samples. This method was based on the MNAzyme-controlled synchronous recognition to EpCAM and CD63 proteins on the membrane of csEVs. Efficient recognition to csEVs via EpCAM aptamer and CD63 aptamer prompted the release of Partzyme A and Partzyme B probes to induce a MNAzyme structure formation, resulting in the cyclic cleavage of substrate chain to produce cascade fluorescence signal amplification. The detection threshold of the developed TESTER approach for csEVs in complicated biological samples was 72 particles μL-1, accomplishing the highly sensitive and selective quantification of csEVs. At the same time, we successfully constructed a new platform for bimolecular simultaneous recognition, which provides a good idea for the construction of bimolecular-activated detection switch in the future.

Electrochemical nucleic acid sensors: Competent pathways for mobile molecular diagnostics

Electrochemical nucleic acid biosensor has demonstrated great promise in clinical diagnostic tests, mainly because of its flexibility, high efficiency, low cost, and easy integration for analytical applications. Numerous nucleic acid hybridization-based strategies have been developed for the design and construction of novel electrochemical biosensors for diagnosing genetic-related diseases. This review describes the advances, challenges, and prospects of electrochemical nucleic acid biosensors for mobile molecular diagnosis. Specifically, the basic principles, sensing elements, applications in diagnosis of cancer and infectious diseases, integration with microfluidic technology and commercialization are mainly included in this review, aiming to provide new insights and directions for the future development of electrochemical nucleic acid biosensors.

Orientation-Controllable Enzyme Cascade on Electrode for Bioelectrocatalytic Chain Reaction

The accomplishment of concurrent interenzyme chain reaction and direct electric communication in a multienzyme-electrode is challenging since the required condition of multienzymatic binding conformation is quite complex. In this study, an enzyme cascade-induced bioelectrocatalytic system has been constructed using solid binding peptide (SBP) as a molecular binder that coimmobilizes the invertase (INV) and flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase gamma-alpha complex (GDHγα) cascade system on a single electrode surface. The SBP-fused enzyme cascade was strategically designed to induce diverse relative orientations of coupling enzymes while enabling efficient direct electron transfer (DET) at the FAD cofactor of GDHγα and the electrode interface. The interenzyme relative orientation was found to determine the intermediate delivery route and affect overall chain reaction efficiency. Moreover, interfacial DET between the fusion GDHγα and the electrode was altered by the binding conformation of the coimmobilized enzyme and fusion INVs. Collectively, this work emphasizes the importance of interenzyme orientation when incorporating enzymatic cascade in an electrocatalytic system and demonstrates the efficacy of SBP fusion technology as a generic tool for developing cascade-induced direct bioelectrocatalytic systems. The proposed approach is applicable to enzyme cascade-based bioelectronics such as biofuel cells, biosensors, and bioeletrosynthetic systems utilizing or producing complex biomolecules.

Enzyme-based electrochemical biosensor for antimonite detection in water

Antimonite (Sb^III) is a naturally occurring contaminant demanding on-site ultrasensitive detection. The enzyme-based electrochemical (EC) biosensors are promising, but the lack of specific Sb^III oxidizing enzymes hindered the past efforts. Herein, we modulated the specificity of arsenite oxidase AioAB toward Sb^III by regulating its spatial conformation from tight to loose using the metal-organic framework ZIF-8. The constructed EC biosensor, AioAB@ZIF-8, exhibited the substrate specificity toward Sb^III at 12.8 s^-1 μM^-1, an order of magnitude higher than that of As^III (1.1 s^-1 μM^-1). Relaxing AioAB structure in ZIF-8 was evidenced by the break of the S-S bond and the conversion of α helix to the random coil as suggested by Raman spectroscopy. Our AioAB@ZIF-8 EC sensor exhibited a dynamic linear range in 0.041-4.1 μM at a response time of 5 s, and the detection limit at 0.041 μM at a high sensitivity of 1894 nA μM^-1. The insights into tuning the specificity of an enzyme shed new light on biosensing metal(loid)s without specific proteins.

Bioconjugation of nanozyme and natural enzyme to enable a one-step cascade reaction for the detection of metabolites

Nanozyme, with enzyme-mimicking activity and excellent stability, has attracted extensive attention. However, some inherent disadvantages, including poor dispersion, low selectivity, and insufficient peroxidase-like activity, still limit its further development. Therefore, an innovative bioconjugation of a nanozyme and natural enzyme was conducted. In the presence of graphene oxide (GO), histidine magnetic nanoparticles (H-Fe₃O₄) were first synthesized by a solvothermal method. The GO-supported H-Fe₃O₄ (GO@H-Fe₃O₄) exhibited superior dispersity and biocompatibility because GO was the carrier and possessed outstanding peroxidase-like activity because of the introduction of histidine. Furthermore, the mechanism of the peroxidase-like activity of GO@H-Fe₃O₄ was the generation of •OH. Uric acid oxidase (UAO) was selected as the model natural enzyme and covalently linked to GO@H-Fe₃O₄ with hydrophilic poly(ethylene glycol) as a linker. UAO could specifically catalyze the oxidation of uric acid (UA) to generate H₂O₂, and subsequently, the newly produced H₂O₂ oxidized the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue ox-TMB under the catalysis of GO@H-Fe₃O₄. Based on the above cascade reaction, the GO@H-Fe₃O₄-linked UAO (GHFU) and GO@H-Fe₃O₄-linked ChOx (GHFC) were used for the detection of UA in serum samples and cholesterol (CS) in milk, respectively. The method based on GHFU exhibited a wide detection range (5-800 μM) and a low detection limit (1.5 μM) for UA, and the method based on GHFC exhibited a wide detection range (4-400 μM) and a low detection limit (1.13 μM) for CS. These results demonstrated that the proposed strategy had great potential in the field of clinical detection and food safety.

Ultrasensitive electrochemical biosensor for detection of circulating tumor cells based on a highly efficient enzymatic cascade reaction

There has been great interest in the enzymatic cascade amplification strategy for the electrochemical detection of circulating tumor cells (CTCs). In this work, we designed a highly efficient enzymatic cascade reaction based on a multiwalled carbon nanotubes-chitosan (MWCNTs-CS) composite for detection of CTCs. A high electrochemical effective surface area was obtained for a MWCNTs-CS-modified glassy carbon electrode (GCE) for loading glucose oxidase (GOD), as well as a high loading rate and high electrical activity of the enzyme. As a 'power source', the MWCNTs-CS composites provided a strong driving power for horseradish peroxidase (HRP) on the surface of polystyrene (PS) microspheres, which acted as probes for capturing CTCs and allowed the reaction to proceed with further facilitation of electron transfer. Aptamer, CTCs, and PS microspheres with HRP and anti-epithelial cell adhesion molecule (anti-EpCAM) antibody were assembled on the MWCNTs-CS/GCE to allow for the modulation of enzyme distance at the micrometer level, and thus ultra-long-range signal transmission was made possible. An ultrasensitive response to CTCs was obtained via this proposed sensing strategy, with a linear range from 10 cell mL^-1 to 6 × 10⁶ cell mL^-1 and a detection limit of 3 cell mL^-1. Moreover, this electrochemical sensor possessed the capability to detect CTCs in serum samples with satisfactory accuracy, which indicated great potential for early diagnosis and clinical analysis of cancer.

Electrochemical biomimetic enzyme cascade amplification combined with target-induced DNA walker for detection of thrombin

Fe-N-doped carbon nanomaterials (Fe-N/CMs) were designed as a novel biomimetic enzyme with excellent peroxidase-like activity to achieve high-efficient enzyme cascade catalytic amplification with the aid of glucose oxidase (GOx), which was further combined with target-induced DNA walker amplification to develop a sensitive electrochemical biosensor for thrombin detection. Impressively, massive output DNA was transformed from small amounts of target thrombin by highly effective DNA walker amplification as protein-converting strategy, which could then induce the immobilization of functionalized nanozyme on the electrode surface to achieve the high-efficient electrochemical biomimetic enzyme cascade amplification. As a result, an amplified enzyme cascade catalytic signal was measured for thrombin detection ranging from 0.01 pM to 1 nM with a low detection limit of 3 fM. Importantly, the new biomimetic enzyme cascade reaction coupled the advantages of natural enzyme and nanozyme, which paved an avenue to construct varied artificial multienzymes amplification systems for biosensing, bioanalysis, and disease diagnosis applications.

Co-Immobilization of GOD & HRP on Y-Shaped DNA Scaffold and the Regulation of Inter-Enzyme Distance

In multienzymes cascade reaction, the inter-enzyme spacing is supposed to be a factor affecting the cascade activity. Here, a simple and efficient Y-shaped DNA scaffold is assembled using two partially complementary DNA single strands on magnetic microspheres, which is used to coimmobilize glucose oxidase (GOD) and horseradish peroxidase (HRP). As a result, on poly(vinyl acetate) magnetic microspheres (PVAC), GOD/HRP-DNA@PVAC multienzyme system is obtained, which can locate GOD and HRP accurately and control the inter-enzyme distance precisely. The distance between GOD and HRP is regulated by changing the length of DNA strand. It showed that the cascade activity is significantly distance-dependent. Moreover, the inter-enzyme spacing is not the closer the better, and too short distance would generate steric hindrance between enzymes. The cascade activity reached the maximum value of 967 U mg^-1 at 13.6 nm, which is 3.5 times higher than that of free enzymes. This is ascribed to the formation of substrate channeling.

A colorimetric and photothermal dual-mode biosensing platform based on nanozyme-functionalized flower-like DNA structures for tumor-derived exosome detection

Tumor-derived exosomes can be served as a kind of promising biomarkers for early diagnosis of cancers. Herein, a colorimetric/photothermal dual-mode exosomes sensing platform is developed for human breast cancer cell (MCF-7)-derived exosomes based on encapsulation of 3,3',5,5'-tetramethylbenzidine-loaded graphene quantum dot nanozymes (TMB-GQDzymes) into DNA flowers (DFs) via rolling circle amplification (RCA). To achieve specific detection, EpCAM aptamer for MCF-7 cell-derived exosomes is immobilized on the well plate, while the complementary sequence of another CD63 aptamer is designed into the circular template to obtain abundant capture probes. Benefitting from the dual-aptamer recognition strategy, a sandwich structure of EpCAM aptamer/exosomes/TMB-GQDzymes@DFs is formed, in which the GQDzymes can catalyze the oxidation of TMB in the presence of H₂O₂. The resulting products of TMB oxidation (oxTMB) can induce not only the absorption changes but also a near-infrared (NIR) laser-driven photothermal effect, achieving dual-mode detection of exosomes with the limit of detection (LOD) of 1027 particles/μL (colorimetry) and 2170 particles/μL (photothermal detection), respectively. In addition, this sensing platform has demonstrated excellent performance to well distinguish breast cancer patients from healthy individuals in serum samples analysis. Overall, the proposed dual-readout biosensor opens promising prospects for exosome detection in biological study and clinical applications.

Label-Free Electrochemical Biosensor Platforms for Cancer Diagnosis: Recent Achievements and Challenges

With its fatal effects, cancer is still one of the most important diseases of today's world. The underlying fact behind this scenario is most probably due to its late diagnosis. That is why the necessity for the detection of different cancer types is obvious. Cancer studies including cancer diagnosis and therapy have been one of the most laborious tasks. Since its early detection significantly affects the following therapy steps, cancer diagnosis is very important. Despite researchers' best efforts, the accurate and rapid diagnosis of cancer is still challenging and difficult to investigate. It is known that electrochemical techniques have been successfully adapted into the cancer diagnosis field. Electrochemical sensor platforms that are brought together with the excellent selectivity of biosensing elements, such as nucleic acids, aptamers or antibodies, have put forth very successful outputs. One of the remarkable achievements of these biomolecule-attached sensors is their lack of need for additional labeling steps, which bring extra burdens such as interference effects or demanding modification protocols. In this review, we aim to outline label-free cancer diagnosis platforms that use electrochemical methods to acquire signals. The classification of the sensing platforms is generally presented according to their recognition element, and the most recent achievements by using these attractive sensing substrates are described in detail. In addition, the current challenges are discussed.

Electrochemical ELASA: improving early cancer detection and monitoring

The discovery of new molecular biomarkers of cancer during the last decades and the development of new diagnostic devices exploiting those have significantly contributed to the clinical analysis of cancer and to improve the outcomes. Among those, liquid biopsy sensors exploiting aptamers for the detection of cancer biomarkers in body fluids are useful and accurate tools for a fast and inexpensive non-invasive screening of population. The incorporation of aptamers in electrochemical sandwich biosensors using enzyme labels, a so-called ELASA, has demonstrated its utility to improve the detection schemes. In this review, we overview the existing ELASA assays for numerous cancer biomarkers as alternatives to the traditional ELISA and discuss their possibilities to reach the market, currently dominated by optical immunoassays.

Electrochemical nano-sensing interface for exosomes analysis and cancer diagnosis

Exosomes are a class of the nanosized extracellular vesicles, which have emerged as representative liquid biopsy biomarkers. To date, the electrochemical nanosensors are of great significance in the exosome detection with the advantages of easy operation, high accuracy and reliable repeatability. Especially, the growing field of nano interface has provided the electrochemical sensing platforms for the accurate exosomes analysis. The incorporation of multiple nanomaterials can take advantages and synergistic properties of functional units. So, based on the integration of with nanomaterial-based signal transduction and specific biorecognition, the nano-sensing interface provides excellent electrochemical features owing to rapid mass transport and excellent conductivity. The nano-sensing interface with a wide variety of morphologies and structure also provides the large active surface area for the immobilization of bio-capturing agents. Furthermore, through the design of nanostructured electrode array, the efficiency of transducer can be greatly improved. It should be noticed that the elaboration of a proper sensor requires the profound knowledge of the nano-sensing interface. Therefore, this article presents a review of the recent advance in exosomes detection based on the electrochemical nano-sensing interface, including electrochemical analysis principles, exosome sensing mechanisms, nano-interface construction strategies, as well as the typical diagnosis application. In particular, the article is focused on the exploration of the various electrochemical sensing performance of nano-interface in the exosome detection. We have also prospected the future trend and challenge of the electrochemical nano-sensing interface for exosomes analysis in clinical cancer diagnosis.

DNA-directed coimmobilization of multiple enzymes on organic−inorganic hybrid DNA flowers

The artificial multienzyme systems developed by mimicking nature has attracted much interest. However, precisely controlled compositions and ratios of multienzymatic co-immobilization systems are still limited by the indistinguishable nature of enzymes. Herein, a strategy for fabricating DNA-directed immobilization of horseradish peroxidase (HRP) and glucose oxidase (GOx) on hybrid DNA nanoflowers (GOx-HRP@hDFs) is presented. The preparation of micron-sized hybrid DNA flowers (hDFs) begins with the predetermined repeatable polymer-like DNA sequences which contained two strands. The hDFs structure is generated through one-pot rolling circle amplification (RCA) and self-assembly with magnesium pyrophosphate inorganic crystals. Based on the rigid-base pairing, GOx and HRP conjugated with sequences complementary to strands would be anchored to the predesigned locations, respectively. By adjusting the loading amount/ratio of enzymes properly, the maximal catalytic efficiency can be precisely regulated. The reaction activity of GOx-HRP@hDFs was 7.4 times higher than that of the free GOx-HRP under the optimal mole ratio (GOx/HRP 4:1). In addition, this multienzyme catalyst system exhibits excellent precision, specificity, reproducibility, and long-term storage stability when applied to real human blood samples. The preceding results validate that GOx-HRP@hDFs are promising candidates for personal diabetes detection.

DNA walker-amplified signal-on electrochemical aptasensors for prostate-specific antigen coupling with two hairpin DNA probe-based hybridization reaction

Electrochemical aptasensing systems have been developed for screening low-abundance disease-related proteins, but most of them involve multiple washings and multi-step separation during measurements, and thus are disadvantageous for routine use. In this work, an innovative and simple electrochemical aptasensing platform was designed for the voltammetric detection of prostate-specific antigen (PSA) in biological fluids without any washing and separation steps. This system mainly included a PSA-specific aptamer, a DNA walker and two hairpin DNA probes (i.e., thiolated hairpin DNA1 and ferrocene-labeled hairpin DNA2). Introduction of target PSA caused the release of the DNA walker from a partially complementary aptamer/DNA walker hybridization strand. The dissociated DNA walker opened the immobilized hairpin DNA1 on the electrode, accompanying subsequent displacement reaction with hairpin DNA2, thus resulting in the DNA walker step-by-step reaction with numerous hairpin DNA1 probes on the sensing interface. In this case, numerous ferrocene molecules were close to the electrode to amplify the voltammetric signal within the applied potentials. All reactions and electrochemical measurements including the target/aptamer reaction and hybridization chain reaction were implemented in the same detection cell. Under optimal conditions, the fabricated electrochemical aptasensor gave good voltammetric responses relative to the PSA concentrations within the range of 0.001-10 ng mL^-1 at an ultralow detection limit of 0.67 pg mL^-1. A good reproducibility with batch-to-batch errors was acquired for target PSA down to 11.5%. Non-target analytes did not interfere with the voltammetric signals of the electrochemical aptasensors. Meanwhile, 15 human serum specimens were measured with electrochemical aptasensors, and displayed well-matched results in comparison with the referenced human PSA enzyme-linked immunosorbant assay (ELISA) method. Significantly, this method provides a new horizon for the quantitative monitoring of low-concentration biomarkers or nucleic acids.

Detection and discrimination of SARS-CoV-2 spike protein-derived peptides using THz metamaterials

The development of effective assay techniques for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has recently received research attention due to its rapid worldwide spread and considerable risk to human health. The receptor-binding domain (RBD) of the spike (S) protein in SARS-CoV-2, a key component for viral entry that has a unique sequence compared to other structural proteins, has been considered an important diagnostic target. In this respect, low-frequency vibrational modes have the advantage of providing information about compositional and structural dependencies at the peptide level. In this study, the sensitive and selective detection of peptides derived from the RBD in SARS-CoV-2 and SARS-CoV was investigated using metamaterial-based sensing chips with a terahertz time-domain spectroscopy (THz-TDS) system. Based on their RBD sequences, two pairs of peptides with 20 residues each were prepared. The sensitivity, specificity, and reproducibility of the proposed system were examined via quantitative analysis using THz metamaterials at three resonance frequencies, and it was found that the species could be discriminated based on their sequences. The THz signals were analyzed with regard to the major amino acid components of the peptides, and the molecular distributions were also investigated based on the hydropathy and net charge of the peptides.

Pd-Fe3O4 Janus nanozyme with rational design for ultrasensitive colorimetric detection of biothiols

Although nanozyme-based colorimetric assays have been broadly used for biosensing, some limitations such as low catalytic activity of nanozyme, poor sensitivity to analytes and lack of understanding the structure-activity relationship remain unsolved. In this work, we developed an ultrasensitive colorimetric method for biothiols detection based on density functional theory-assisted design of janus Pd-Fe₃O₄ nanozyme. The Pd-Fe₃O₄ dumbbell-like nanoparticles (DBNPs) prepared by seed-mediated approach shows a uniform heterodimeric nanostructure. Ultrasensitive biothiols detection is achieved from two aspects. On one hand, due to the synergistic effect between Pd and Fe₃O₄ in the dumbbell structure, Pd-Fe₃O₄ DBNPs show enhanced peroxidase-mimic activity compared to the individual components. On the other hand, when the target biothiols molecule is present, its inhibition effect on the janus Pd-Fe₃O₄ nanozyme is also significantly enhanced. The above results are confirmed both in experiment and theoretical calculation. Based on the rational design, a simple, highly selective and urtrasensitive colorimetric and quantitative assay for biothiols is developed. The limit of detection (LOD) can reach as low as 3.1 nM in aqueous solution. This assay is also successfully applied to the detection of biothiols in real urine samples. Moreover, the Pd-Fe₃O₄ nanozyme is used to discriminate biothiols levels in normal and cancer cells with high sensitivity at the cell density of 15,000/mL, which demonstrates its great potential in biological and clinical analysis. This work not only shows the great promise of janus bimetallic nanozymes' excellent functionalities but also provides rational guidelines to design high-performance nanozymes for biosensing and biomedical applications.

Dual-strategy biosensing of glucose based on multifunctional CuWO4 nanoparticles

The multifunctional CuWO4 NPs were prepared and exhibit large specific surface area, good conductivity and excellent peroxidase-like activity, which was exploited for electrochemical and colorimetric dual-strategy biosensing of glucose.

A colorimetric aptasensor based on a hemin/EpCAM aptamer DNAzyme for sensitive exosome detection

Exosomes are considered as potential biomarkers that can reflect information from their parent cell-associated cancer microenvironment.

Technological advances in electrochemical biosensors for the detection of disease biomarkers

With an increasing focus on health in contemporary society, interest in the diagnosis, treatment, and prevention of diseases has grown rapidly. Accordingly, the demand for biosensors for the early diagnosis of disease is increasing. However, the measurement range of existing electrochemical sensors is relatively high, which is not suitable for early disease diagnosis, requiring the detection of small amounts of biocomponents. Various attempts have been made to overcome this and amplify the signal, including binding with various labeling molecules, such as DNA, enzymes, nanoparticles, and carbon materials. Efforts are also being made to increase the sensitivity of electrochemical sensors, and the combination of nanomaterials, materials, and biotechnology offers the potential to increase sensitivity in a variety of ways. Recent studies suggest that electrochemical sensors can be a powerful tool in providing comprehensive insights into the targeting and detection of disease-associated biomarkers. Significant advances in nanomaterial and biomolecule approaches for improved sensitivity have resulted in the development of electrochemical biosensors capable of detecting multiple biomarkers in real time in clinically relevant samples. In this review, we have discussed the recent studies on electrochemical sensors for detection of diseases such as diabetes, degenerative diseases, and cancer. Further, we have highlighted new technologies to improve sensitivity using various materials, including DNA, enzymes, nanoparticles, and carbon materials.

Machine Learning-Reinforced Noninvasive Biosensors for Healthcare

The emergence and development of noninvasive biosensors largely facilitate the collection of physiological signals and the processing of health-related data. The utilization of appropriate machine learning algorithms improves the accuracy and efficiency of biosensors. Machine learning-reinforced biosensors are started to use in clinical practice, health monitoring, and food safety, bringing a digital revolution in healthcare. Herein, the recent advances in machine learning-reinforced noninvasive biosensors applied in healthcare are summarized. First, different types of noninvasive biosensors and physiological signals collected are categorized and summarized. Then machine learning algorithms adopted in subsequent data processing are introduced and their practical applications in biosensors are reviewed. Finally, the challenges faced by machine learning-reinforced biosensors are raised, including data privacy and adaptive learning capability, and their prospects in real-time monitoring, out-of-clinic diagnosis, and onsite food safety detection are proposed.

Aptamer and bifunctional enzyme co-functionalized MOF-derived porous carbon for low-background electrochemical aptasensing

To improve the efficiency of aptasensors, a signal amplification strategy by coupling tyrosinase (Tyr)-triggered redox cycling with nanoscale porous carbon (NCZIF) has been proposed. The NCZIF was obtained by calcining ZIF-8 crystals in an inert atmosphere. It had high surface areas, great biocompatibility, and ease of functionalization, which was beneficial for immobilizing sufficient Tyr and aptamer covalently. When the target prostate-specific antigen (PSA) was present, the NCZIF functionalized with Tyr and an aptamer bound to the aptamer-modified Au electrode specifically through the sandwich structure. Then, Tyr acted to oxidize the electroinactive phenol, which led to low-background signal, in the substrate to electroactive catechol, and triggered the redox cycling under the action of NADH. The low detection limit of the proposed electrochemical aptasensor for PSA was 0.01 ng mL^-1, and the wide detection range was from 0.01 to 50 ng mL^-1. The use of ZIF-8 derived porous carbon and Tyr-triggered redox cycling system provided a promising solution for the development of simple, rapid, reliable, and low-background aptasensing methods, which had great potential in the field of disease diagnosis and biomedicine.

Ternary Electrochemiluminescence Biosensor Based on DNA Walkers and AuPd Nanomaterials as a Coreaction Accelerator for the Detection of miRNA-141

In this study, a ternary electrochemiluminescence (ECL) sensing platform coupled with a multiple signal amplification strategy was proposed for ultrasensitive detection of miRNA-141. The initial signal amplification was achieved via three-dimensional reduced graphene oxide (3D-rGO)@Au nanoparticles (NPs) to form an excellent conductive layer. Then, AuPd NPs as a coreaction accelerator was introduced into the N-(4-aminobutyl)-N-(ethylisoluminol) (ABEI)-H₂O₂ system to facilitate the transformation from H₂O₂ to excess superoxide anion radicals (O₂^•-), which further amplified the ECL emission of ABEI, leading to a significant increase of the ECL signal. Meanwhile, in the presence of miRNA-141 and T7 Exonuclease (T7 Exo), the self-assembled DNA swing arm can be driven to walk autonomously. The DNA walker reaction could result in the release of numerous labeled luminophores, which could react to achieve an extremely weak ECL signal. Surprisingly, the established ECL sensor platform for the detection of miRNA-141 demonstrated excellent sensitivity with a low detection limit of 31.9 aM in the concentration range from 100 aM to 1 nM. Consequently, the designed strategy greatly improves the luminous efficiency of the ternary ECL system and provides a special approach for the detection of nucleic acids and biomarkers in clinical and biochemical analysis.