Iron, Nitrogen-Doped Carbon Aerogels for Fluorescent and Electrochemical Dual-Mode Detection of Glucose

Multimodal biosensing systems based on metal nanoparticles

Biosensors are currently among the most commonly used devices for analysing biomarkers and play an important role in environmental detection, food safety, and disease diagnosis. Researchers have developed multimodal biosensors instead of single-modal biosensors to meet increasing sensitivity, accuracy, and stability requirements. Metal nanoparticles (MNPs) are beneficial for preparing core probes for multimodal biosensors because of their excellent physical and chemical properties, such as easy regulation and modification, and because they can integrate diverse sensing strategies. This review mainly summarizes the excellent physicochemical properties of MNPs applied as biosensing probes and the principles of commonly used MNP-based multimodal sensing strategies. Recent applications and possible improvements of multimodal biosensors based on MNPs are also described, among which on-site inspection and sensitive detection are particularly important. The current challenges and prospects for multimodal biosensors based on MNPs may provide readers with a new perspective on this field.

Atomic Engineering of Single-Atom Nanozymes for Biomedical Applications

Single-atom nanozymes (SAzymes) showcase not only uniformly dispersed active sites but also meticulously engineered coordination structures. These intricate architectures bestow upon them an exceptional catalytic prowess, thereby captivating numerous minds and heralding a new era of possibilities in the biomedical landscape. Tuning the microstructure of SAzymes on the atomic scale is a key factor in designing targeted SAzymes with desirable functions. This review first discusses and summarizes three strategies for designing SAzymes and their impact on reactivity in biocatalysis. The effects of choices of carrier, different synthesis methods, coordination modulation of first/second shell, and the type and number of metal active centers on the enzyme-like catalytic activity are unraveled. Next, a first attempt is made to summarize the biological applications of SAzymes in tumor therapy, biosensing, antimicrobial, anti-inflammatory, and other biological applications from different mechanisms. Finally, how SAzymes are designed and regulated for further realization of diverse biological applications is reviewed and prospected. It is envisaged that the comprehensive review presented within this exegesis will furnish novel perspectives and profound revelations regarding the biomedical applications of SAzymes.

A novel highly active AgMOF-based silver single-atom catalyst and its application to the aptamer SERS/RRS for the determination of aflatoxin B1

A novel highly active silver single-atom catalyst (AgSAC) was prepared by a microwave-assisted solvothermal method using silver covalent organic frameworks (AgMOF) as precursors. It was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared (IR), and surface-enhanced Raman scattering (SERS). The experiment found that AgSAC has excellent catalytic performance and can heavily catalyze the nano-reaction of chloroauric acid-malic acid (HAuCl4-H2Mi) to generate gold nanoparticles (AuNPs). The produced AuNPs have strong SERS, resonance Rayleigh scattering (RRS) and surface plasmon resonance absorption (Abs) signals. Aflatoxin B1 aptamer (AptAFB1) can be adsorbed to the surface of AgSAC through electrostatic interaction, to reduce the catalytic activity of AgSAC and the SERS/RRS/Abs signal of the system. When the target molecule (AFB1) was added, it will specifically bind to AptAFB1 and release AgSAC, restoring the catalytic activity of AgSAC, thereby restoring the SERS/RRS/Abs signal of the system. Based on this, a simple and sensitive aptamer sensing analysis platform for trace AFB1 was established, and a reasonable catalytic amplification mechanism of AgSAC was proposed. The SERS method exhibited the highest sensitivity, with a linear range of 0.005-0.225 μg/L and a detection limit of 0.002 μg/L.

Multi-modal nanoprobe-enabled biosensing platforms: a critical review

Nanomaterials show great potential for applications in biosensing due to their unique physical, chemical, and biological properties. However, the single-modal signal sensing mechanism greatly limits the development of single-modal nanoprobes and their related sensors. Multi-modal nanoprobes can realize the output of fluorescence, colorimetric, electrochemical, and magnetic signals through composite nanomaterials, which can effectively compensate for the defects of single-modal nanoprobes. Following the multi-modal nanoprobes, multi-modal biosensors break through the performance limitation of the current single-modal signal and realize multi-modal signal reading. Herein, the current status and classification of multi-modal nanoprobes are provided. Moreover, the multi-modal signal sensing mechanisms and the working principle of multi-modal biosensing platforms are discussed in detail. We also focus on the applications in pharmaceutical detection, food and environmental fields. Finally, we highlight this field's challenges and development prospects to create potential enlightenment.

Dual-mode fluorescence and electrochemiluminescence sensors based on Ru-MOF nanosheets for sensitive detection of apoE genes

A fluorescence-electrochemiluminescence (FL-ECL) dual-mode sensor for apoE gene detection has been developed, leveraging the unique properties of ruthenium metal organic framework nanosheets (RuMOFNSs). The system utilizes the quenching effect of the Ru(bpy)32+ ECL signal by ferrocene, leading to the synthesis of a multi-electron electrical signal marker, bisferrocene. By immobilizing the P-DNA on RuMOFNSs, bisferrocene quenches both FL and ECL signals. The addition of T-DNA and the consequent formation of double-stranded DNA enable the ExoIII enzyme to excise the bisferrocene fragment, restoring the signals. The sensor demonstrates wide detection linear ranges (1 fM to 1 nM for FL and 0.01 fM to 10 pM for ECL) and remarkable sensitivity (0.048 fM for FL and 0.016 fM for ECL). The dual-mode design offers enhanced reliability through a self-correction feature, reducing false positives. Compared to single-mode sensors, the dual-mode sensor shows significant advantages. Real-world testing confirms the sensor's capacity for robust detection in actual samples, underscoring its promising application in early disease diagnosis. This innovative approach opens up avenues for multi-signal response sensors, offering significant potential for diagnostic technologies.

A dual-mode sensor platform with adjustable electrochemiluminescence-fluorescence for selective detection of paraquat pesticide

This study presents functionalized metal-organic frameworks nanosheets (RuMOFNSs) with strong electrochemiluminescence (ECL) and fluorescence (FL) properties and a novel signal marker-tetraferrocene. Based on the efficient quenching effect of the tetraferrocene on RuMOFNSs, a "signal switch" ECL-FL dual-mode sensor is constructed for sensitive detection of paraquat (PQ). ECL and FL signals are annihilated after adding paraquat-aptamer DNA (PQ-Apt DNA) labeled with tetraferrocene since it is close to RuMOFNSs. PQ is added, and the strong binding and intermolecular interaction between PQ-Apt DNA and PQ induces spatial separation, with tetraferrocene groups far away from RuMOFNSs. At this point, ECL and FL signals are restored. The change in ECL and FL signals realized the quantitative determination of the PQ solution. In addition, the dual-mode sensor exhibits high sensitivity and specificity with detection limits as low as 0.008 ng/mL and 0.059 ng/mL. The proposed sensor is successfully applied to determine PQ, indicating its great application potential in the food industry.

CdSe/TiO2NTs Heterojunction-Based Nonenzymatic Photoelectrochemical Sensor for Glucose Detection

Compared with a single semiconductor, the heterojunction formed by two different semiconductors usually has higher light utilization and better photoelectric performance. By using stable TiO2 nanotubes as the main subject, CdSe/TiO2NTs heterojunctions were synthesized by a hydrothermal method. XRD, TEM, SEM, PL, UV-vis, and EIS were used to characterize the fabricated CdSe/TiO2NTs. Under visible light irradiation, CdSe/TiO2NTs heterojunctions exhibited a higher absorption intensity and lower degree of photogenerated carrier recombination than TiO2. The electrons and holes were proven to be effectively separated in this heterojunction via theoretical calculation. Under CdSe/TiO2NTs' optimal conditions, the glucose concentrations (10-90 μM) had a linear relationship with the photocurrent value, and the detection limit was 3.1 μM. Moreover, the CdSe/TiO2NTs sensor exhibited good selectivity and stability. Based on the experimental data and theoretical calculations, its PEC sensing mechanism was also illuminated.

Dual-Mode Ratiometric Electrochemical and Turn-On Fluorescent Detection of Butyrylcholinesterase Utilizing a Single Probe for the Diagnosis of Alzheimer's Disease

Biomarkers detection in blood with high accuracy is crucial for the diagnosis and treatment of many diseases. In this study, the proof-of-concept fabrication of a dual-mode sensor based on a single probe (Re-BChE) using a dual-signaling electrochemical ratiometric strategy and a "turn-on" fluorescent method is presented. The probe Re-BChE was synthesized in a single step and demonstrated dual mode response toward butyrylcholinesterase (BChE), a promising biomarker of Alzheimer's disease (AD). Due to the specific hydrolysis reaction, the probe Re-BChE demonstrated a turn-on current response for BChE at -0.28 V, followed by a turn-off current response at -0.18 V, while the fluorescence spectrum demonstrated a turn-on response with an emission wavelength of 600 nm. The developed ratiometric electrochemical sensor and fluorescence detection demonstrated high sensitivity with BChE concentrations with a low detection limit of 0.08 μg mL^-1 and 0.05 μg mL^-1, respectively. Importantly, the dual-mode sensor presents the following advantages: (1) dual-mode readout can correct the impact of systematic or background error, thereby achieving more accurate results; (2) the responses of dual-mode readout originate from two distinct mechanisms and relatively independent signal transduction, in which there is no interference between two signaling routes. Additionally, compared with the reported single-signal electrochemical assays for BChE, both redox potential signals were detected in the absence of biological interference within a negative potential window. Furthermore, it was discovered that the outcomes of direct dual-mode electrochemical and fluorescence quantifications of the level of BChE in serum were in agreement with those obtained from the use of commercially available assay kits for BChE sensing. This method has the potential to serve as a useful point-of-care tool for the early detection of AD.

High-loading Cu single-atom nanozymes supported by carbon nitride with peroxidase-like activity for the colorimetric detection of tannic acid

The design of nanozymes with high metal atom loading is of great significance to improve enzyme activity and is also the key to furthering the construction of highly sensitive colorimetric sensors. In this work, a colorimetric sensor for the quantitative analysis of tannic acid (TA) was developed based on two-dimensional carbon nanosheet carbon nitride (CN)-supported Cu single-atom nanozymes (Cu/CN). Cu/CN was synthesized by supramolecular preorganization and calcination, with an ultrathin nanosheet structure and a high density of Cu active sites, with a Cu loading of up to 14.3 wt%. Benefiting from the above characteristics, Cu/CN exhibits peroxidase-mimicking activity and excellent catalytic performance. Therefore, a colorimetric sensor was constructed for the fast and sensitive quantitative analysis of TA with good linearity in the range of 0.09-3.2 μM and a low detection limit of 30 nM. Furthermore, the sensor was successfully applied to the analysis of TA in tea samples of different varieties. This work sheds new light on the design of nanozymes with a high density of active sites and the analysis of TA in real environments.

Light-enhanced transparent hydrogel for uric acid and glucose detection by four different analytical platforms

The lack of solid-phase media limits the portability of colorimetric sensing platforms. In this study, a series of transparent polyvinyl alcohol (PVA) hydrogels encapsulated antimony tin oxide nanoparticles (ATO NPs) and 3,3',5,5'-tetramethylbenzidine (TMB) were developed as the solid-phase sensing media for glucose and uric acid. Under the conditions of H₂O₂ and UV light, the hydrogel presented a multicatalytic ability (photo Fenton-like and peroxidase-like activities), which accelerated the oxidation of TMB, turning the hydrogel from colorless to blue and finally enhancing the detection signal. The plasticity of the hydrogel allowed it to be designed into various shapes (membrane, microsphere etc.) to adapt multiple detection platforms (a liquid/solid-phase UV spectrophotometer, a NanoPhotometer, and smartphone spectroscopy). The hydrogel sensing media exhibited excellent tunability and enhanced the photocatalytic ability. The proposed material was successfully applied to detect glucose and uric acids in real samples by four detection platforms to evaluate its practicability.

Mechanism and Application of Surface-Charged Ferrite Nanozyme-Based Biosensor toward Colorimetric Detection of l-Cysteine

Peroxidase-like nanozymes with robust catalytic capacity and detection specificity have been proposed as substitutes to natural peroxidases in biochemical sensing. However, the catalytic activity enhancement, detection mechanism, and application of nanozyme-based biosensors toward l-cysteine (l-Cys) detection still remain significant challenges. In this work, a doped ferrite nanozyme with well-defined structure and surface charges is fabricated by a two-step method of continuous flow coprecipitation and high-temperature annealing. The resulted ferrite nanozyme possesses an average size of 54.5 nm and a zeta-potential of 6.45 mV. A high-performance biosensor is manufactured based on the peroxidase-like catalytic feature of the doped ferrite. The ferrite nanozyme can oxidize the 3,3',5,5'-tetramethylbenzidine (TMB) with the assistance of H₂O₂ because of the instinctive capacity to decompose H₂O₂ into ·OH. The Michaelis-Menten constants (0.0911 mM for TMB, 0.140 mM for H₂O₂) of the ferrite nanozyme are significantly smaller than those of horseradish peroxidase. A reliable colorimetric method is established to selectively analyze l-Cys via a facile mixing-and-detecting methodology. The detection limit and linear range are 0.119 μM and 0.2-20 μM, respectively. Taking the merits of the ferrite nanozyme-based biosensors, the l-Cys level in the human serum can be qualitatively detected. It can be anticipated that the surface-charged ferrite nanozyme shows great application prospects in the fields of bioanalytical chemistry and point-of-care testing.

Polymer Carbon Nanodots: A Novel Electrochemiluminophore for Dual Mode Detection of Ferric Ions

The development of simple and effective dual-mode analytical methods plays crucial regulatory roles in the discrimination of relevant target species, because of their built-in cross reference correction and high accuracy. In this work, a novel polymer carbon nanodots (PCNDs) prepared from a facile one-pot hydrothermal procedure using readily available l-tryptophan and l-phenylalanine as precursors, showed excellent aqueous solubility and blue fluorescence property with a high quantum yield of 29%. Moreover, the PCNDs was demonstrated to be a robust luminophore with electrochemiluminescence (ECL) efficiency of 43% was achieved by using K₂S₂O₈ as a coreactant. The spooling ECL spectroscopy was employed to take insight into excited states responsible for the potential-dependent ECL emissions. Most importantly, when introduced into construction of the fluorescence and ECL dual mode sensing platform, for the first time, the PCNDs displayed prominent performance for the detection of ferric ions (Fe³⁺). The ferric ions could be quantified ranging from micromolar to millimolar with a detection limit of 0.22 and 5.3 μM, respectively. Such a dual-functional sensing platform also exhibits excellent selectivity, reproducibility and stability. Results from this work indicate that PCNDs showing great promise as a bright luminophore for the fabrication of low-cost, high-performance dual-signal readout platforms for ferric ions determination.