Enzyme‐Encapsulated DNA Hydrogel for Highly Efficient Electrochemical Sensing Glucose

Application of smart-responsive hydrogels in nucleic acid and nucleic acid-based target sensing: A review

In recent years, nucleic acid-related sensing and detection have become essential in clinical diagnostics, treatment and genotyping, especially in connection with the Human Genome Project and the COVID-19 pandemic. Many traditional nucleic acid-related sensing strategies have been employed in analytical chemistry, including fluorescence, colorimetric and chemiluminescence methods. However, their key limitation is the lack of understanding of the interaction during analysis, particularly at the 3D matrix level close to biological tissue. To address this issue, smart-responsive hydrogels are increasingly used in biosensing due to their hydrophilic and biocompatible properties. By combining smart-responsive hydrogels with traditional nucleic acid-related sensing, biological microenvironments can be mimicked, and targets can be easily accessed and diffused, making them ideal for nucleic acid sensing. This review focuses on utilizing smart-responsive hydrogels for nucleic acid-related sensing and detection, including nucleic acid detection, other nucleic acid-based analyte detection and nucleic acid-related sensing platforms applying nucleic acid as sensing tools in hydrogels. Additionally, the analytical mechanisms of smart-responsive hydrogels with the combination of various detection platforms such as optical and electrochemical techniques are described. The limitations of using smart-responsive hydrogels in nucleic acid-related sensing and proposed possible solutions are also discussed. Lastly, the future challenge of smart-responsive hydrogels in nucleic acid-related sensing is explored. Smart-responsive hydrogels can be used as biomimetic materials to simulate the extracellular matrix, achieve biosensing, and exhibit great potential in nucleic acid-related sensing. They serve as a valuable complement to traditional detection and analytical methods.

Three-Dimensional DNA Hydrogel Mediated Dual-Mode Sensing Method for Quantification of Epithelial Cell Adhesion Molecule in Biological Fluid Samples

Monitoring changes in the expression of marker proteins in biological fluids is essential for biomarker-based disease diagnosis. Epithelial cell adhesion molecule (EpCAM) has been identified as a broad-spectrum biomarker for various chronic diseases and as a therapeutic target. However, the development of simple and reliable methods for quantifying EpCAM changes in biological fluids faces challenges due to the variability of its expression across different diseases, the presence of soluble forms, and matrix effects. In this paper, a surface-enhanced Raman scattering (SERS)-fluorescence (FL) dual-mode sensing method was established for quantification of trace EpCAM in biological fluids based on bimetallic Au@Ag nanoparticles and nitrogen-doped quantum dots encapsulated DNA hydrogel hybrid with graphene oxide (Au@Ag-NQDs/GO). The DNA hydrogel was constructed based on three-dimensional (3D) structure DNA-mediated strategy using an aptamer DNA (AptDNA) linker. The interaction of the AptDNA with EpCAM triggered the disassembly of the DNA hydrogel. Consequently, the release of Au@Ag nanoparticles induced an "on-off" switch in the SERS signal while the weakened FL quenching effect in Au@Ag-NQDs/GO system achieved "off-on" switch of FL signal, enabling the simultaneous SERS-FL quantification of EpCAM. The established dual-mode method exhibited outstanding sensitivity and stability in quantifying EpCAM in the range of 0.5-60.0 pg/mL, with the limits of detection (LODs) of SERS and FL as 0.17 and 0.35 pg/mL, respectively. When applied for real sample analysis, the method showed satisfactory specificity and recoveries in cancer cells lysate, serum, and urine samples with RSDs of 2.8-6.3%, 4.0-6.3%, and 2.8-5.7%, respectively. The developed SERS-FL sensing method offered a sensitive, reliable, and practical quantification strategy for trace EpCAM in diverse biological fluid samples, which would benefit the early diagnosis of disease and further health management.

Digital multimeter-based portable photoelectrochemical immunoassay with enzyme-catalyzed precipitation for screening carbohydrate antigen 125

The degree of the carbohydrate antigen 125 (CA-125) level in serum is positively correlated with the severity of ovarian cancer. In this study, a facile photoelectrochemical (PEC) immunoassay was devised for sensitive detection of CA-125 employing enzyme-catalyzed precipitation to weaken the photocurrent of hollow porous In2O3 nanotubes incorporating CdS nanoparticles. Upon the addition of the target analyte, horseradish peroxidase (HRP) enriches as a result of the formation of the sandwich immunocomplex, which can catalyze the conversion of 4-chloro1-naphthol (4-CN) to benzo-4-chlorohexadienone (4-CD) employing H2O2 as a cofactor. The as-produced insoluble precipitate acts as an obstacle to hinder the absorption of visible light by photoactive materials, thereby resulting in a decrease in photocurrent. Moreover, the weakened signal can be easily read out by a digital multimeter (DMM), advancing the convenience of the detection system. The preliminary analysis data indicate that the PEC immunoassay shows an efficient response to CA-125 levels ranging from 0.1 to 100 U mL-1 with a limit of detection (LOD) as low as 0.046 U mL-1 (S/N = 3). Most importantly, the proposed portable method has shown satisfactory performance in terms of selectivity, reproducibility, stability, and analysis in complex biological matrices.

Supercritical carbon dioxide technology in food processing: Insightful comprehension of the mechanisms of microbial inactivation and impacts on quality and safety aspects

Supercritical carbon dioxide (SC-CO2) has emerged as a nonthermal technology to guarantee food safety. This review addresses the potential of SC-CO2 technology in food preservation, discussing the microbial inactivation mechanisms and the impact on food products' quality parameters and bioactive compounds. Furthermore, the main advantages and gaps are denoted. SC-CO2 technology application causes adequate microbial reductions (>5 log cfu/mL) of spoilage and pathogenic microorganisms, enzyme inactivation, and improvements in the storage stability in fruit and vegetable products (mainly fruit juices), meat products, and dairy derivatives. SC-CO2-treated products maintain the physicochemical, technological, and sensory properties, bioactive compound concentrations, and biological activity (antioxidant and angiotensin-converting enzyme-inhibitory activities) similar to the untreated products. The optimization of processing parameters (temperature, pressure, CO2 volume, and processing times) is mandatory for achieving the desired results. Further studies should consider the expansion to different food matrices, shelf-life evaluation, bioaccessibility of bioactive compounds, and in vitro and in vivo studies to prove the benefits of using SC-CO2 technology. Moreover, the impact on sensory characteristics and, mainly, the consumer perception of SC-CO2-treated foods need to be elucidated. We highlight the opportunity for studies in postbiotic production. In conclusion, SC-CO2 technology may be used for microbial inactivation to ensure food safety without losing the quality parameters.

Recent advances in hydrogel microneedle-based biofluid extraction and detection in food and agriculture

Microneedle (MN) technology has been extensively studied for its advantages of minimal invasiveness and user-friendliness. Notably, hydrogel microneedles (HMNs) have garnered considerable attention for biofluid extraction due to its high swelling properties and biocompatibility. This review provides a comprehensive overview of definition, materials, and fabrication methods associated with HMNs. The extraction mechanisms and optimization strategies for enhancing extraction efficiency are summarized. Moreover, particular emphasis is placed on HMN-based biofluid extraction and detection in the domains of food and agriculture, encompassing the detection of small molecules, nucleic acids, and other relevant analytes. Finally, current challenges and possible solutions associated with HMN-based biofluid extraction are discussed.

Probing the influence of crosslinkers on the properties, response, and degradation of enzymatic hydrogels for electrochemical glucose biosensing through fluorescence analysis

Drop-cast crosslinked hydrogels are a common platform for enzymatic electrochemical biosensors. Despite the widespread use of these complex systems, there are still several questions about how their physicochemical properties affect their performance, stability, and reproducibility. In this work, first-generation faradaic biosensors composed of glucose oxidase and branched polyethyleneimine (BPEI) are prepared using either glutaraldehyde (GA) or ethylene glycol diglycidyl ether (EGDGE) as crosslinkers. While EGDGE gels present an increasing electrochemical response with increasing crosslinker concentration, the current of GA gels decreases at high crosslinker concentration probably due to the hampered diffusion on tightly networked gels. We compared different strategies to use fluorescence microscopy to gain insight into the gel structure either by labeling the gel components with fluorophores or taking advantage of the intrinsic fluorescence of the imines formed upon crosslinking with GA. By monitoring the fluorescence of the crosslinking bonds and the electrochemical response, we demonstrate that hydrolysis, a common hydrogel degradation mechanism, is not responsible for the loss of electrical current over time in gels prepared with glutaraldehyde. Most hydrogel-based electrochemical biosensor studies do not perform specific experiments to determine the cause of the degradation and instead just infer it from the dependence of the current on the preparation conditions (most commonly concentrations). We show that, by taking advantage of several analytical techniques, it is possible to gain more knowledge about the degradation mechanisms and design better enzymatic biosensors.

Alanine aminotransferase electrochemical sensor based on graphene@MXene composite nanomaterials

Graphene@MXene composite nanomaterials were utilized to construct an electrochemical sensor for alanine aminotransferase (ALT) detection. The combination of graphene nanosheets with MXene avoids the self-stacking of MXene and graphene, and broadens the charge transfer channel. In addition, the composite nanomaterial provides increased loading sites for pyruvate oxidase. The principle of ALT detection is a two-step enzymatic reaction. L-Alanine was initially transferred to pyruvate catalyzed by ALT. The formed pyruvate was then oxidized by pyruvate oxidase, generating H2O2. Through the detection of the generated H2O2, ALT activity was measured. The linear range of the sensor to ALT was from 5 to 400 U·L-1 with a detection limit of 0.16 U·L-1 (S/N = 3). For real sample analysis, the spiked recovery test results of ALT in serum samples were between 96.89 and 103.93% with RSD < 5%, confirming the reliability of the sensor testing results and potential clinical application of the sensor.

Novel Enzymatic Biosensor Utilizing a MoS2/MoO3 Nanohybrid for the Electrochemical Detection of Xanthine in Fish Meat

A rapid, reliable, and user-friendly electrochemical sensor was developed for the detection of xanthine (Xn), an important biomarker of food quality. The developed sensor is based on a nanocomposite comprised of molybdenum disulfide-molybdenum trioxide (MoS2/MoO3) and synthesized using a single-pot hydrothermal method. Structural analysis of the MoS2/MoO3 nanocomposite was conducted using X-ray diffraction (XRD) and Raman spectroscopy, while its compositional properties were evaluated through X-ray photoelectron spectroscopy (XPS). Morphological features were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Two-dimensional (2D) MoS2 offers advantages such as a high surface-to-volume ratio, biocompatibility, and strong light-matter interaction, whereas MoO3 serves as an effective electron transfer mediator and exhibits excellent stability in aqueous environments. The enzymatic biosensor derived from this nanocomposite demonstrates remarkable cyclic stability and a low limit of detection of 64 nM. It enables rapid, reproducible, specific, and reproducible detection over 10 cycles while maintaining a shelf life of more than 5 weeks. These findings highlight the potential of our proposed approach for the development of early detection devices for Xn.

Spinal cord injury immunosensor: Sensitive detection of S100β on interdigitated electrode sensor

A spinal cord injury is damage to the nerves and cells that receive and provide a signal from the brain to the rest of the body. Spinal injury causes changes in movement, sensation, and strength, affect the body functions near the injury site, and may lead to paralysis. S100β was found as a suitable biomarker for identifying spinal cord injury and its causing problem. Herein, S100β immunoassay was developed on interdigitated electrode sensor to diagnose spinal cord injury. For effective anti-S100β antibody immobilization, the antibody was premixed with 3-Aminopropyl)triethoxsilane and then attached to the hydroxylated interdigitated electrode surface. This method of antibody immobilization enhanced the antibody attachment two-times than the method without premix. Antibody-attached surfaces increased current responses as S100 concentrations increased, and the limit of detection was seen to be 1 pg/mL on the linearity until 3000 pg/mL at an R2 value of 0.9907 [y = 7x - 6.4667]. Further, biofouling experiments with glial fibrillary acidic protein and γ-aminobutyric acid failed to enhance the current response, indicating the specific detection of S100β. This immunoassay identifies S100β at its lower level and helps to diagnose spinal cord injury and its related problem.

Investigation of the Impact of Hydrogen Bonding Degree in Long Single-Stranded DNA (ssDNA) Generated with Dual Rolling Circle Amplification (RCA) on the Preparation and Performance of DNA Hydrogels

DNA hydrogels have gained significant attention in recent years as one of the most promising functional polymer materials. To broaden their applications, it is critical to develop efficient methods for the preparation of bulk-scale DNA hydrogels with adjustable mechanical properties. Herein, we introduce a straightforward and efficient molecular design approach to producing physically pure DNA hydrogel and controlling its mechanical properties by adjusting the degree of hydrogen bonding in ultralong single-stranded DNA (ssDNA) precursors, which were generated using a dual rolling circle amplification (RCA)-based strategy. The effect of hydrogen bonding degree on the performance of DNA hydrogels was thoroughly investigated by analyzing the preparation process, morphology, rheology, microstructure, and entrapment efficiency of the hydrogels for Au nanoparticles (AuNPs)-BSA. Our results demonstrate that DNA hydrogels can be formed at 25 °C with simple vortex mixing in less than 10 s. The experimental results also indicate that a higher degree of hydrogen bonding in the precursor DNA resulted in stronger internal interaction forces, a more complex internal network of the hydrogel, a denser hydrogel, improved mechanical properties, and enhanced entrapment efficiency. This study intuitively demonstrates the effect of hydrogen bonding on the preparation and properties of DNA hydrogels. The method and results presented in this study are of great significance for improving the synthesis efficiency and economy of DNA hydrogels, enhancing and adjusting the overall quality and performance of the hydrogel, and expanding the application field of DNA hydrogels.

Focus Review on Nanomaterial-Based Electrochemical Sensing of Glucose for Health Applications

Diabetes management can be considered the first paradigm of modern personalized medicine. An overview of the most relevant advancements in glucose sensing achieved in the last 5 years is presented. In particular, devices exploiting both consolidated and innovative electrochemical sensing strategies, based on nanomaterials, have been described, taking into account their performances, advantages and limitations, when applied for the glucose analysis in blood and serum samples, urine, as well as in less conventional biological fluids. The routine measurement is still largely based on the finger-pricking method, which is usually considered unpleasant. In alternative, glucose continuous monitoring relies on electrochemical sensing in the interstitial fluid, using implanted electrodes. Due to the invasive nature of such devices, further investigations have been carried out in order to develop less invasive sensors that can operate in sweat, tears or wound exudates. Thanks to their unique features, nanomaterials have been successfully applied for the development of both enzymatic and non-enzymatic glucose sensors, which are compliant with the specific needs of the most advanced applications, such as flexible and deformable systems capable of conforming to skin or eyes, in order to produce reliable medical devices operating at the point of care.

Advances in the Translation of Electrochemical Hydrogel-Based Sensors

Novel biomaterials for bio- and chemical sensing applications have gained considerable traction in the diagnostic community with rising trends of using biocompatible and lowly cytotoxic material. Hydrogel-based electrochemical sensors have become a promising candidate for their swellable, nano-/microporous, and aqueous 3D structures capable of immobilizing catalytic enzymes, electroactive species, whole cells, and complex tissue models, while maintaining tunable mechanical properties in wearable and implantable applications. With advances in highly controllable fabrication and processability of these novel biomaterials, the possibility of bio-nanocomposite hydrogel-based electrochemical sensing presents a paradigm shift in the development of biocompatible, "smart," and sensitive health monitoring point-of-care devices. Here, recent advances in electrochemical hydrogels for the detection of biomarkers in vitro, in situ, and in vivo are briefly reviewed to demonstrate their applicability in ideal conditions, in complex cellular environments, and in live animal models, respectively, to provide a comprehensive assessment of whether these biomaterials are ready for point-of-care translation and biointegration. Sensors based on conductive and nonconductive polymers are presented, with highlights of nano-/microstructured electrodes that provide enhanced sensitivity and selectivity in biocompatible matrices. An outlook on current challenges that shall be addressed for the realization of truly continuous real-time sensing platforms is also presented.

A Label-Free Photoelectrochemical Biosensor Based on CRISPR/Cas12a System Responsive Deoxyribonucleic Acid Hydrogel and "Click" Chemistry

A novel label-free photoelectrochemical (PEC) biosensor is presented in this work. As a barrier, the DNA hydrogel could block the coupling between g-C₃N₄ and CdS quantum dots (QDs). Therefore, extremely low photocurrent signals were obtained. The presence of target microRNA-21 can initiate the rolling circle amplification (RCA) reaction, which in turn produces many repeated sequences to activate the CRISPR/Cas12a system. The trans-cleavage activity of the CRISPR/Cas12a system led to the degradation of DNA hydrogels efficiently. As a result, the g-C₃N₄/CdS QDs heterojunction was formed through "click" chemistry. Through the amplification of the RCA and CRISPR/Cas12a system, the sensitivity of the PEC biosensor was improved significantly with the detection limit of 3.2 aM. The proposed sensor also showed excellent selectivity and could be used to detect actual samples. In addition, the modular design could facilitate the detection of different objects. Thus, the proposed CRISPR/Cas12a system responsive DNA hydrogel provides a simple, sensitive, and flexible way for label-free PEC analysis.

A carbon dots-enhanced laccase-based electrochemical sensor for highly sensitive detection of dopamine in human serum

Enzyme-based electrochemical sensor possesses a significant advantage in the highly efficient detection of small molecules, however, the poor electron transport efficiency limits their wide application. In this study, taking advantage of the distinct biocatalytic activity of laccase and the excellent electroconductibility of carbon dots, a carbon dots-enhanced laccase-based electrochemical sensor for the detection of dopamine (DA) is established. Thereinto, laccase can specifically recognize DA and promote its electrocatalytic oxidation on the electrode, while, the carbon dots can be used as the immobilization substrate of laccase and enhance its electron transfer efficiency, thus achieving the highly sensitive detection of dopamine. The electrochemical performance of the modified electrode interface is studied by electrochemical impedance spectroscopy and differential pulse voltammetry. As demonstrated, the electrocatalytic activity of the proposed electrochemical sensor for DA is significantly improved and exhibits a low detection limit (0.08 μM) and a wide linear range (0.25 μM-76.81 μM). The excellent selectivity allows the sensor has the capacity for specific discrimination the DA from other interferents. Furthermore, by analyzing the DA in human serum verifies the practicability of this assay in real sample analysis.

Smartphone-Based Photoelectrochemical Immunoassay with Co9S8@ZnIn2S4 for Point-of-Care Diagnosis of Breast Cancer Biomarker

Photoelectrochemical immunoassays incorporating specific antigen-antibody recognition reactions with the photon-electron conversion capabilities of photocatalysts have been developed for biomarker detection, but most involve bulky and expensive equipment and are unsuitable for point-of-care testing. Herein, a portable smartphone-based photoelectrochemical immunoassay was innovatively designed for the on-site detection of breast cancer biomarkers (human epidermal growth factor receptor 2; HER2). The system consists of a split-type immunoassay mode, disposable screen-printed electrode covered with hierarchical Co9S8@ZnIn2S4 heterostructures, an integrated circuit board, and a Bluetooth smartphone equipped with a specially designed app. Using alkaline phosphatase (ALP) catalytic strategy to in situ generate ascorbic acid (AA) for electron-donating toward Co9S8@ZnIn2S4 heterostructures, an immunoreaction was successfully constructed for the HER2 detection in the real sample due to the positive correlation of the photocurrent signal to electron donor concentration. Differential charge density indicates that the formation of Co9S8@ZnIn2S4 heterojunction can facilitate the flow of charges in the interface and enhance the photocurrent of the composite. More importantly, the measured photocurrent signal can be wirelessly transmitted to the software and displayed on the smartphone screen to obtain the corresponding HER2 concentration value. The photocurrent values linearly with the logarithm of HER2 concentrations range spanned from 0.01 ng/mL to 10 ng/mL with a detection limit of 3.5 pg/mL. Impressively, the clinical serum specimen results obtained by the proposed method and the wireless sensing device are in good agreement with the enzyme-linked immunosorbent assay (ELISA).

Biosensor Based on Covalent Organic Framework Immobilized Acetylcholinesterase for Ratiometric Detection of Carbaryl

A ratiometric electrochemical biosensor based on a covalent organic framework (COF_Thi-TFPB) loaded with acetylcholinesterase (AChE) was developed. First, an electroactive COF_Thi-TFPB with a two-dimensional sheet structure, positive charge and a pair of inert redox peaks was synthesized via a dehydration condensation reaction between positively charged thionine (Thi) and 1,3,5-triformylphenylbenzene (TFPB). The immobilization of AChE on the positively charged electrode surface was beneficial for maintaining its bioactivity and achieving the best catalytic effect; therefore, the positively charged COF_Thi-TFPB was an appropriate support material for AChE. Furthermore, the COF_Thi-TFPB provided a stable internal reference signal for the constructed AChE inhibition-based electrochemical biosensor to eliminate various effects which were unrelated to the detection of carbaryl. The sensor had a linear range of 2.2–60 μM with a detection limit of 0.22 μM, and exhibited satisfactory reproducibility, stability and anti-interference ability for the detection of carbaryl. This work offers a possibility for the application of COF-based materials in the detection of low-level pesticide residues.

Hydrogels as functional components in artificial cell systems

Recent years have seen substantial efforts aimed at constructing artificial cells from various molecular components with the aim of mimicking the processes, behaviours and architectures found in biological systems. Artificial cell development ultimately aims to produce model constructs that progress our understanding of biology, as well as forming the basis for functional bio-inspired devices that can be used in fields such as therapeutic delivery, biosensing, cell therapy and bioremediation. Typically, artificial cells rely on a bilayer membrane chassis and have fluid aqueous interiors to mimic biological cells. However, a desire to more accurately replicate the gel-like properties of intracellular and extracellular biological environments has driven increasing efforts to build cell mimics based on hydrogels. This has enabled researchers to exploit some of the unique functional properties of hydrogels that have seen them deployed in fields such as tissue engineering, biomaterials and drug delivery. In this Review, we explore how hydrogels can be leveraged in the context of artificial cell development. We also discuss how hydrogels can potentially be incorporated within the next generation of artificial cells to engineer improved biological mimics and functional microsystems.

Photoelectrochemical bioanalysis of microRNA on yolk-in-shell Au@CdS based on the catalytic hairpin assembly-mediated CRISPR-Cas12a system

This work reports on the proof-of-concept of a photoelectrochemical (PEC) biosensor with a horseradish peroxidase-single stranded DNA-encoded magnetic bead (MB-ssDNA-HRP) signal probe cleaved by the catalytic hairpin assembly (CHA)-mediated clustered regularly interspaced short palindromic repeats (CRISPR)-Cas12a system for the quantification of microRNA (miR-21) by using yolk-in-shell Au@CdS as a photoactive material.

Amorphous metal-organic frameworks on PtCu hydrogels: Enzyme immobilization platform with boosted activity and stability for sensitive biosensing

Cell-free enzymatic catalysis (CFEC) is emerging biotechnology that simulates biological transformations without living cells. However, the high cost of separation and preparation of the enzyme has hindered the practical application of the CFEC. Enzyme immobilization technologies using solid supports to stabilize enzymes have been regarded as an efficient strategy to address this issue. Nevertheless, the activity and stability of the immobilized enzymes are still crucial challenges for working in vitro. Herein, an enzyme immobilization platform is developed by using PtCu hydrogels coated with amorphous metallic-organic frameworks (MOFs) as multifunctional carriers to encapsulate horseradish peroxidase (HRP). Specifically, PtCu hydrogels acting as a "reservoir of metal ions" can interact with the immobilized enzyme and facilitate electron transfer, leading to the boosted enzyme catalytic performances. Furthermore, amorphous MOFs on the surface of PtCu hydrogels serve as an "armor" to protect the internal enzymes from various perturbation environments. The resultant enzyme immobilization platform (PtCu@HRP@ZIF-8) not only shows an approximately 2.4-fold enhanced activity compared with free enzyme but also exhibits improved stability against harsh conditions. The PtCu@HRP@ZIF-8-based biosensor is constructed for sensitive sensing of organophosphorus pesticides (OPs). The proposed biosensor exhibits a favorable linear relationship with the concentration of paraoxon-ethyl from 6 to 800 ng/mL, with a low detection limit of 1.8 ng/mL. This work reveals the promising potential of our proposed enzyme immobilization platform in practical applications.

Photoelectrochemical sandwich immunoassay of CYFRA21-1 based on In2O3/WO3 type-II heterojunction and CdS quantum dots-polydopamine nanospheres labeling

Using an In₂O₃/WO₃ type-II heterojunction modified fluorine-doped tin oxide (FTO) electrode as the photoanode and CdS quantum dots (QDs)-polydopamine nanospheres (PDA NSs) as the secondary antibody (Ab₂) label, the photoelectrochemistry (PEC) sandwich immunosensing of the lung cancer marker CYFRA21-1 was studied. WO₃ nanoplates were prepared by a hydrothermal method, In₂O₃ nanoporous spheres were prepared by a hydrothermal method followed by calcination, and the In₂O₃/WO₃ type-II heterojunction with high PEC activity was prepared by ultrasonic mixing and cast-coating. PDA NSs with a high surface area can be loaded with abundant Ab₂ molecules and many CdS QDs with an energy level well matched with the heterojunction, so the photocurrent signal can be amplified by the formation of a sandwich immunostructure. Through the simulation experiments of photoelectrode-modified chitosan films of varying thickness, the effective transport distance of photogenerated charges is preliminarily discussed. Under the optimized conditions, the photocurrent was linear with the common logarithm of CYFRA21-1 concentration from 100 fg mL^-1 to 50 ng mL^-1, with a limit of detection of 56 fg mL^-1 (S/N = 3). The immunoassay of CYFRA21-1 in human serum samples gave satisfactory recovery results.

Biosensing human blood clotting factor by dual probes: Evaluation by deep long short-term memory networks in time series forecasting

Artificial intelligence of things (AIoT) has become a potential tool for use in a wide range of fields, and its use is expanding in interdisciplinary sciences. On the other hand, in a clinical scenario, human blood-clotting disease (Royal disease) detection has been considered an urgent issue that has to be solved. This study uses AIoT with deep long short-term memory networks for biosensing application and analyzes the potent clinical target, human blood clotting factor IX, by its aptamer/antibody as the probe on the microscaled fingers and gaps of the interdigitated electrode. The earlier results by the current-volt measurements have shown the changes in the surface modification. The limit of detection (LOD) was noticed as 1 pM with the antibody as the probe, whereas the aptamer behaved better with the LOD at 100 fM. The time-series predictions from the AIoT application supported the obtained results with the laboratory analyses using both probes. This application clearly supports the results obtained from the interdigitated electrode sensor as aptamer to be the better option for analyzing the blood clotting defects. The current study supports a great implementation of AIoT in sensing application and can be followed for other clinical biomarkers.

CRISPR-Cas12a-Derived Photoelectrochemical Biosensor for Point-Of-Care Diagnosis of Nucleic Acid

This work presented a point-of-care (POC) photoelectrochemical (PEC) biosensing for the detection of human papillomavirus-16 (HPV-16) on a portable electrochemical detection system by using CRISPR-Cas12a trans-cleaving the G-quadruplex for the biorecognition/amplification and a hollow In₂O₃-In₂S₃-modified screen-printed electrode (In₂O₃-In₂S₃/SPE) as the photoactive material. G-quadruplexes were capable of biocatalytic precipitation (H₂O₂-mediated 4-chloro-1-naphthol oxidation) on the In₂O₃-In₂S₃/SPE surface, resulting in a weakened photocurrent, but suffered from trans-cleavage when the CRISPR-Cas12a system specifically recognized the analyte. The photocurrent results could be directly observed with the card-sized electrochemical device via a smartphone, which displayed a high-value photocurrent for these positive samples, while a low-value photocurrent for the target-free samples. Such a system exhibited satisfying photocurrent responses toward HPV-16 within a wide working range from 5.0 to 5000 pM and allowed for detection of HPV-16 at a concentration as low as 1.2 pM. The proposed assay provided a smartphone signal readout to enable the rapid screening PEC determination of HPV-16 concentration without sophisticated instruments, thus meeting the requirements of remote areas and resource-limited settings. We envision that combining an efficient biometric PEC sensing platform with a wireless card-sized electrochemical device will enable high-throughput POC diagnostic analysis.

Applications of scaffold-based advanced materials in biomedical sensing

There have been many efforts to synthesize advanced materials that are capable of real-time specific recognition of a molecular target, and allow the quantification of a variety of biomolecules. Scaffold materials have a porous structure, with a high surface area and their intrinsic nanocavities can accommodate cells and macromolecules. The three-dimensional structure (3D) of scaffolds serves not only as a fibrous structure for cell adhesion and growth in tissue engineering, but can also provide the controlled release of drugs and other molecules for biomedical applications. There has been a limited number of reports on the use of scaffold materials in biomedical sensing applications. This review highlights the potential of scaffold materials in the improvement of sensing platforms and summarizes the progress in the application of novel scaffold-based materials as sensor, and discusses their advantages and limitations. Furthermore, the influence of the scaffold materials on the monitoring of infectious diseases such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and bacterial infections, was reviewed.

CRISPR/Cas12a-mediated liposome-amplified strategy for the photoelectrochemical detection of nucleic acid

This study reports a photoelectrochemical biosensor for dopamine-loaded liposome-encoded magnetic beads cleaved by clustered regularly interspaced short palindromic repeats (CRISPR)/Cas 12a system for the quantification of human papilloma virus (HPV)-related DNA using neodymium-doped BiOBr nanosheets (Nd-BiOBr) as a photoactive matrix. Magnetic beads and dopamine-loaded liposomes are covalently attached to the both ends of ssDNA to construct dumbbell-shaped dopamine-loaded liposome-encoded magnetic bead (DLL-MB) probes. When the guide RNA binds to the target HPV-16, the ssDNA will be cleaved by Cas12a, thereby degrading the double dumbbell probes. After magnetic separation, the dissolved DLLs are treated with Triton X-100 to release the dopamine (as an electron donor), which was then detected by an amplified photocurrent using the Nd-BiOBr-based photoelectrode.

Development, Preparation, and Biomedical Applications of DNA-Based Hydrogels

Hydrogels have outstanding research and application prospects in the biomedical field. Among them, the design and preparation of biomedical hydrogels with deoxyribonucleic acid (DNA) as building blocks have attracted increasing research interest. DNA-based hydrogel not only has the skeleton function of hydrogel, but also retains its biological functions, including its excellent selection specificity, structural designability, precise molecular recognition ability, outstanding biocompatibility, and so on. It has shown important application prospects in the biomedical field, such as drug delivery, biosensing, and tissue engineering. In recent years, researchers have made full use of the characteristics of DNA molecules and constructed various pure DNA-based hydrogels with excellent properties through various crosslinking methods. Moreover, via introducing functional molecules or elements, or combining with other functional materials, a variety of multifunctional DNA-based hybrid hydrogels have also been constructed, which expand the breadth and depth of their applications. Here, we described the recent development trend in the area of DNA-based hydrogels and highlighted various preparation methods of DNA-based hydrogels. Representative biomedical applications are also exemplified to show the high performance of DNA-based hydrogels. Meanwhile, the existing problems and prospects are also summarized. This review provided references for the further development of DNA-based hydrogels.

Sensitive silica-alumina modified capacitive non-Faradaic glucose sensor for gestational diabetes

A highly sensitive silica-alumina (Si-Al)-modified capacitive non-Faradaic glucose biosensor was introduced to monitor gestational diabetes. Glucose oxidase (GOx) was attached to the Si-Al electrode surface as the probe through amine-modification followed by glutaraldehyde premixed GOx as aldehyde-amine chemistry. This Si-Al (∼50 nm) modified electrode surface has increased the current flow upon binding of GOx with glucose. Capacitance values were increased by increasing the glucose concentrations. A mean capacitance value was plotted and the detection limit was found as 0.03 mg/mL with the regression coefficient value, R² = 0.9782 [y = 0.8391x + 1.338] on the linear range between 0.03 and 1 mg/mL. Further, a biofouling experiment with fructose and galactose did not increase the capacitance, indicating the specific glucose detection. This Si-Al-modified capacitance sensor detects a lower level of glucose presence and helps in monitoring gestational diabetes.

Rice-Spikelet-like Copper Oxide Decorated with Platinum Stranded in the CNT Network for Electrochemical In Vitro Detection of Serotonin

The specific monitoring of serotonin (ST) has provoked massive interest in therapeutic and biological science since it has been recognized as the third most significant endogenous gastrointestinal neurotransmitter. Hence, there is a great need to develop a sensitive and low-cost sensing platform for the detection of a clinically relevant ST level in biological matrices. Herein, we develop a simple two-step approach for an ultrasensitive electrochemical (EC) sensor with the Cu₂O metal oxide (MO)-incorporated CNT core that has been further deposited with a transitional amount of platinum nanoparticles (Pt NPs). We presented, for the first time, the deposition of Pt NPs on the (CNTs-Cu₂O-CuO) nanopetal composite via the galvanic replacement method, where copper not only acts as a reductant but a sacrificial template as well. The electrocatalytic aptitude of the fabricated EC sensing platform has been assessed for the sensitive detection of ST as a proficient biomarker in early disease diagnostics. The synergy of improved active surface area, remarkable conductivity, polarization effect induced by Pt NPs on CNTs-Cu₂O-CuO nanopetals, fast electron transfer, and mixed-valence states of copper boost up the redox processes at the electrode-analyte junction. The CNTs-Cu₂O-CuO@Pt-modified electrode has unveiled outstanding electrocatalytic capabilities toward ST oxidation in terms of a low detection limit of 3 nM (S/N = 3), wide linear concentration range, reproducibility, and incredible durability. Owing to the amazing proficiency, the proposed EC sensor based on the CNTs-Cu₂O-CuO@Pt heterostructure has been applied for ST detection in biotic fluids and real-time tracking of ST efflux released from various cell lines as early disease diagnostic approaches.

Surfactant-free liquid-exfoliated copper hydroxide nanocuboids for non-enzymatic electrochemical glucose detection

To facilitate printable sensing solutions particles need to be suspended and stabilised in a liquid medium. Hansen parameters were used to identify that alcohol-water blends are ideal for stabilising colloidal copper hydroxide in dispersion. The suspended material can be further separated in various size fractions with a distinct cuboid geometry which was verified using atomic force microscopy. This facilitates the development of Raman spectroscopic metrics for determining particle sizes. This aspect ratio is related to the anisotropic crystal structure of the bulk crystallites. As the size of the nanocuboids decreases electrochemical sensitivity of the material increases due to an increase in specific surface area. Electrochemical glucose sensitivity was investigated using both cyclic voltammetry and chronoamperometry. The sensitivity is noted to saturate with film thickness. The electrochemical response of 253 mA M^-1 cm^-2 up to 0.1 mM and 120 mA cm^-2 up to 0.6 mM allow for calibration of potential devices. These results indicate suitability for use as a glucose sensor and, due to the surfactant-free, low boiling point solvent approach used to exfoliate the nanocuboids, it is an ideal candidate for printable solutions. The ease of processing will also allow this material to be integrated in composite films for improved functionality in future devices.