Carbon dots based photoelectrochemical sensors for ultrasensitive detection of glutathione and its applications in probing of myocardial infarction

Carbon-based photoelectrochemical sensors: recent developments and future prospects

Owing to the considerable potential of photoelectrochemical (PEC) sensors, they have gained significant attention in the analysis of biological, environmental, and food markers. However, the limited charge mass transfer efficiency and rapid recombination of electron hole pairs have become obstacles in the development of PEC sensors. In this case, considering the unique advantages of carbon-based materials, they can be used as photosensitizers, supporting materials and conductive substrates and coupled with semiconductors to prepare composite materials, solving the above problems. In addition, there are many types of carbon materials, which can have semiconductor properties and form heterojunctions after coupling with semiconductors, effectively promoting the separation of electron hole pairs. Herein, we aimed to provide a comprehensive analysis of reports on carbon-based PEC sensors by introducing their research and application status and discussing future development trends in this field. In particular, the types and performance improvement strategies of carbon-based electrodes and the working principles of carbon-based PEC sensors are explained. Furthermore, the applications of carbon-based photoelectric sensors in environmental monitoring, biomedicine, and food detection are highlighted. Finally, the current limitations in the research on carbon-based PEC sensors are emphasized and the need to enhance the sensitivity and selectivity through material modification, structural design, improved device performance, and other strategies are emphasized.

Application of surface nitrogen-doped graphene quantum dots in the sensing of ferric ions and glutathione: Spectroscopic investigations and DFT calculations

Developing a sensing platform that can quickly and accurately measure glutathione (GSH) is crucial for the early detection of various human diseases. GQDs have shown great potential in many technological and biological applications. This study focused on synthesizing nitrogen-doped GQDs (NGQDs) with stable blue fluorescence using a simple and easy hydrothermal method in one step. The bamboo fiber was used as the green source for this synthesis. The NGQDs had a tiny particle size of 4.7 nm and emitted light at 405 nm when excited. They displayed a remarkable quantum yield of 40.36 % and were effectively used as fluorescent probe to specifically detect Fe3+. The energy transfer mechanism led to the NGQDs' fluorescence being deactivated by Fe3+ ions (turn- "off"). However, with the addition of GSH to the system, the fluorescence intensity of NGQDs was reactivated (turn- "on"). Thus, a fluorescence turn "off-on" system was developed for the sensitive detection of Fe3+ and GSH. Using density functional theory (DFT), it was theoretically calculated that the surface of the fabricated NGQDs possess lone pairs of electrons on oxygens and doped nitrogen causing a photo-induced electron transfer (PET) process to occur. This PET process was suppressed previously owing to complex formation between oxygen atoms of modeled structure and ferric ions. The sensing platform displayed a sensitive response to Fe3+ in the 1-1000 μM range with LOD of 34 nM and GSH in the range of 1-50 μM, with a detection limit of 45 nM. Furthermore, the NGQDs exhibited high selectivity towards Fe3+ and GSH over other electrolytes and biomolecules. Additionally, the probe exhibited non-cytotoxicity and was practically applicable for the detection of GSH in HeLa cells.

Constructing DNAzyme-driven three-dimensional DNA nanomachine-mediated paper-based photoelectrochemical device for ultrasensitive detection of miR-486-5p

As a unique class of dynamic nanostructures, biomimetic DNA walking machines that exhibit geometrical complexity and nanometre precision have gained great success in photoelectrochemical (PEC) bioanalysis. Despite certain achievements, the slow reaction kinetics and low processivity severely restrict the amplification efficiency of the DNA walker-mediated biosensors. Herein, by taking advantage of efficient DNA rolling machines, a three-dimensional (3D) DNA nanomachine-mediated paper-based PEC device for speedy ultrasensitive detection of miR-486-5p was successfully constructed. To achieve it, a novel In2S3/SnS2 sensitized heterojunction was firstly in-situ grown on the Au-modified paper fibers and implemented as the photoanode with effective separation of photogenerated carriers to achieve an enhanced initial photocurrent. Subsequently, the copper hexacyanoferrate(II)-modified CuO nanosphere was introduced as a multifunctional signal regulator via the competitive capture of electron donors and photon energy with the photoelectric layer for efficiently quenching the PEC signal. With the introduction of targets, the DNAzyme-driven DNA nanomachine with editable motion modes was gradually activated and it could continuously cleave the tracks DNA labeled quenching probes, finally achieving the recovery of PEC signal. As a proof of concept, the elaborated paper-based PEC device presented a wide linear range from 0.1 fM to 100 pM and a detection limit of 35 aM for miR-486-5p bioassay. This work provides an innovative insight to the exploitation of DNA nanobiotechnology and nucleic acid signal amplification strategy.

Molecularly imprinted ultrasensitive cholesterol photoelectrochemical sensor based on perfluorinated organics functionalization and hollow carbon spheres anchored organic-inorganic perovskite

In spite of organic-inorganic perovskite emerging as a novel efficient light-harvesting material owing to their superior optical properties, excitonic properties, and electrical conductivity, the related applications are severely limited for their poor stability and selectivity. Herein, we introduced hollow carbon spheres (HCSs) and 2-(perfluorohexyl) ethyl methacrylate (PFEM) based molecularly imprinted polymers (MIPs) to dual-functionalize CH3NH3PbI3. HCSs can provide perovskite load conditions, passivate perovskite defects, increase carrier transport and effectively improve its hydrophobicity. The perfluorinated organic compound based MIPs film can not only enhance the water and oxygen stability of perovskite, but also endow it specific selectivity. Moreover, it can reduce the photoexcited electron-hole pair recombination and prolong the electron lifetime. Benefiting from the synergistic sensitization of HCSs and MIPs, an ultrasensitive photoelectrochemical platform (MIPs@CH3NH3PbI3@HCSs/ITO) for cholesterol sensing was acquired with a very wide linear range of 5.0 × 10-14-5.0 × 10-8 mol/L and an extremely low detection limit of 2.39 × 10-15 mol/L. The designed PEC sensor exhibited good selectivity and stability, as well as practicality for real sample analysis. The present work extended the development of the high-performance perovskite and showed its broad application prospect for advanced PEC construction.

Latest advances in biomimetic nanomaterials for diagnosis and treatment of cardiovascular disease

Cardiovascular disease remains one of the leading causes of death in China, with increasingly serious negative effects on people and society. Despite significant advances in preventing and treating cardiovascular diseases, such as atrial fibrillation/flutter and heart failure over the last few years, much more remains to be done. Therefore, developing innovative methods for identifying and managing cardiovascular disorders is critical. Nanomaterials provide multiple benefits in biomedicine, primarily better catalytic activity, drug loading, targeting, and imaging. Biomimetic materials and nanoparticles are specially combined to synthesize biomimetic nanoparticles that successfully reduce the nanoparticles' toxicity and immunogenicity while enhancing histocompatibility. Additionally, the biological targeting capability of nanoparticles facilitates the diagnosis and therapy of cardiovascular disease. Nowadays, nanomedicine still faces numerous challenges, which necessitates creating nanoparticles that are highly selective, toxic-free, and better clinically applicable. This study reviews the scientific accomplishments in this field over the past few years covering the classification, applications, and prospects of noble metal biomimetic nanozymes and biomimetic nanocarriers.

Ligands engineering of gold nanoclusters with enhanced photoluminescence for deceptive information encryption and glutathione detection

Gold nanoclusters (Au NCs) have appeared as an essential alternative to traditional quantum dots and fluorescent molecules for the development of intelligent stimuli-responsive photoluminescence (PL), but the low PL emission of Au NCs restricts their broad applications. Herein, we reported a simple yet effective strategy for preparing Au NCs with high PL by ligands engineering of 4-hydroxy-2-mercapto-6-methylpyrimidine (MTU) and L-Arginine (Arg). Owing to the rigidified shell and the ligand-to-metal charge transfer (LMCT) effects, it was found that the assembly of Arg ligand on MTU-protected Au NCs (Arg/MTU-Au NCs) led to a significantly enhanced PL in the alkaline solution up to 30 times. Moreover, utilizing the tunable LMCT, the Arg/MTU-Au NCs displayed rapid responses to multi-type ionic interaction in a reversible manner, such as H+/OH- and Cu2+/glutathione (GSH) pairs. Inspired by these intriguing ions-responsive LMCT and the associated switchable PL emission, the Arg/MTU-Au NCs were successfully used as excellent stimuli-responsive PL probes for intriguing deceptive information encryption and biosensing as well. This work would provide new insight into regulating the PL emission of Au NCs by ligands engineering and advance their potential applications in information encryption and bioassay.

CdS-Modified TiO2 Nanotubes with Heterojunction Structure: A Photoelectrochemical Sensor for Glutathione

The formation of heterojunction structures can effectively prevent the recombination of photogenerated electron-hole pairs in semiconductors and result in the enhancement of photoelectric properties. Using TiO₂ nanotubes (prepared using the hydrothermal-impregnation method) as carriers, CdS-TiO₂NTs were fabricated as a photoelectrochemical (PEC) sensor, which can be used under visible light and can exhibit good PEC performance due to the existence of the heterojunction structure. The experimental results show that the prepared CdS-TiO₂NTs electrode had a linear response to 2-16 mM glutathione (GSH). The sensor's sensitivity and detection limit (LOD) were 102.9 µA·mM^-1 cm^-2 and 27.7 µM, respectively. Moreover, the biosensor had good stability, indicating the potential application of this kind of heterojunction PEC biosensor.

Nanozyme Based on Dispersion of Hemin by Graphene Quantum Dots for Colorimetric Detection of Glutathione

Compared with natural enzymes, nanozymes have the advantages of good catalytic performance, high stability, low cost, and can be used under extreme conditions. Preparation of highly active nanozymes through simple methods and their application in bioanalysis is highly desirable. In this work, a nanozyme based on dispersion of hemin by graphene quantum dot (GQD) is demonstrated, which enables colorimetric detection of glutathione (GSH). GQD was prepared by a one-step hydrothermal synthesis method. Hemin, the catalytic center of heme protein but with low solubility and easy aggregation that limits its catalytic activity, can be dispersed with GQD by simple sonication. The as-prepared Hemin/GQD nanocomplex had excellent peroxidase-like activity and can be applied as a nanozyme. In comparison with natural horseradish peroxidase (HRP), Hemin/GQD nanozyme exhibited a clearly reduced Michaelis–Menten constant (K_m) when tetramethylbenzidine (TMB) was used as the substrate. With H₂O₂ being the substrate, Hemin/GQD nanozyme exhibited a higher maximum reaction rate (V_max) than HRP. The mechanisms underlying the nanozyme activity were investigated through a free radical trapping experiment. A colorimetric platform capable of sensitive detection of GSH was developed as the proof-of-concept demonstration. The linear detection range was from 1 μM to 50 μM with a low limit of detection of 200 nM (S/N = 3). Determination of GSH in serum samples was also achieved.

Ultrasensitive and Selective Detection of Glutathione by Ammonium Carbamate-Gold Platinum Nanoparticles-Based Electrochemical Sensor

Determining the concentration of glutathione is crucial for developing workable medical diagnostic strategies. In this paper, we developed an electrochemical sensor by electrodepositing amino-based reactive groups and gold–platinum nanomaterials on the surface of glassy carbon electrode successively. The sensor was characterized by cyclic voltammetry (CV), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), and electrochemical impedance spectra (EIS). Results showed that Au@Pt nanoparticles with the size of 20–40 nm were presented on the surface of electrode. The sensor exhibits excellent electrocatalytic oxidation towards glutathione. Based on this, we devised an electrochemical biosensor for rapid and sensitive detection of glutathione. After optimizing experimental and operational conditions, a linear response for the concentration of GSH, in the range of 0.1–11 μmol/L, with low detection and quantification limits of 0.051 μM (S/N = 3), were obtained. The sensor also exhibits superior selectivity, reproducibility, low cost, as well as simple preparation and can be applied in human serum sample detection.

Nanomaterials-Mediated Therapeutics and Diagnosis Strategies for Myocardial Infarction

The alarming mortality and morbidity rate of myocardial infarction (MI) is becoming an important impetus in the development of early diagnosis and appropriate therapeutic approaches, which are critical for saving patients' lives and improving post-infarction prognosis. Despite several advances that have been made in the treatment of MI, current strategies are still far from satisfactory. Nanomaterials devote considerable contribution to tackling the drawbacks of conventional therapy of MI by improving the homeostasis in the cardiac microenvironment via targeting, immune modulation, and repairment. This review emphasizes the strategies of nanomaterials-based MI treatment, including cardiac targeting drug delivery, immune-modulation strategy, antioxidants and antiapoptosis strategy, nanomaterials-mediated stem cell therapy, and cardiac tissue engineering. Furthermore, nanomaterials-based diagnosis strategies for MI was presented in term of nanomaterials-based immunoassay and nano-enhanced cardiac imaging. Taken together, although nanomaterials-based strategies for the therapeutics and diagnosis of MI are both promising and challenging, such a strategy still explores the immense potential in the development of the next generation of MI treatment.

A Yellow Fluorescence Probe for the Detection of Oxidized Glutathione and Biological Imaging

It is well-known that the ratio of reduced l-glutathione (GSH) to oxidized l-glutathione (GSSG) is a vital biomarker for monitoring overall cellular health, thus detecting the intracellular concentration of glutathione is of great significance. Recently, an increasing number of reports have published various methods for GSH detection, but studies on the detection of GSSG are still rare. Here, we report a kind of new yellow fluorescent carbon dots (CDs) for the detection of GSSG through a fluorescence "off-on" process. Because the surface is rich in amino groups, the CDs show a positive potential. When the concentration of GSSG was continuously increased, the CDs' fluorescence dropped sharply, while the fluorescence gradually recovered after the addition of sodium sulfide. The phenomenon of fluorescence quenching is linear with the concentration of the quencher (GSSG)(0-200 μM), and 0.18 μM is calculated as the detection limit. More interestingly, as a fluorescent probe, the CDs can be further used for fluorescence imaging in living cells and zebrafish.

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

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

A novel design of multiple ligands for ultrasensitive colorimetric chemosensor of glutathione in plasma sample

In this study, we developed a novel colorimetric chemosensor for selective and sensitive recognition of Glutathione (GSH) using a simple binary mixture of commercially accessible and inexpensive metal receptors with names, Bromo Pyrogallol Red (BPR) and Xylenol Orange (XO). This procedure is based on the synergistic coordination of BPR and XO with cerium ion (Ce3+) for the recognition of GSH over other available competitive amino acids (AAs) especially thiol species in aqueous media. Generally, cysteine (Cys) and homocysteine (hCys) can seriously interfere with the detection of GSH among common biological species because they possess similar chemical behavior. Using all the information from 1HNMR and FT-IR studies, the proposed interaction is presented in which GSH acts as a tri-dentate ligand with three N donor atoms in conjunction with BPR and XO as mono and bi-dentate ligands respectively. This approach opens a path for selective detection of other AAs by argumentatively selecting the ensemble of mixed organic ligands from commercially available reagents, thereby eliminating the need for developing synthetic receptors, sample preparation, organic solvent mixtures, and expensive equipment. Evaluating the feasibility of the existing method was led to the determination of GSH in human plasma samples.

Integration detection of mercury(ii) and GSH with a fluorescent "on-off-on" switch sensor based on nitrogen, sulfur co-doped carbon dots

Using aurine and citric acid as precursors, we have synthesized stable blue-fluorescent nitrogen and sulfur co-doped carbon dots (NS-CDs), with a high quantum yield of up to 68.94% via a thermal lysis method. The fluorescent NS-CDs were employed as a sensitive sensor for the integration detection of Hg2+ and glutathione (GSH). This was attributed to Hg2+ effectively quenching the fluorescence of the NS-CDs by static quenching, and then GSH was able to recover the fluorescence owing to the stronger binding between Hg2+ and the sulfhydryl of GSH. Based on the "on-off-on" tactic, the detection limits of Hg2+ ions and GSH were 50 nM and 67 nM respectively. The fluorescence sensor was successfully applied to detect Hg2+ ions and GSH in actual samples (tap water and fetal bovine serum). Furthermore, we have proved that the sensor had good reversibility. Overall, our NS-CDs can serve as effective sensors for environmental and biological analysis in the future.

Carbon dots for virus detection and therapy

Recent experience with the COVID-19 pandemic should be a lesson learnt with respect to the effort we have to invest in the development of new strategies for the treatment of viral diseases, along with their cheap, easy, sensitive, and selective detection. Since we live in a globalized world where just hours can play a crucial role in the spread of a virus, its detection must be as quick as possible. Thanks to their chemical stability, photostability, and superior biocompatibility, carbon dots are a kind of nanomaterial showing great potential in both the detection of various virus strains and a broad-spectrum antiviral therapy. The biosensing and antiviral properties of carbon dots can be tuned by the selection of synthesis precursors as well as by easy post-synthetic functionalization. In this review, we will first summarize current options of virus detection utilizing carbon dots by either electrochemical or optical biosensing approaches. Secondly, we will cover and share the up-to-date knowledge of carbon dots' antiviral properties, which showed promising activity against various types of viruses including SARS-CoV-2. The mechanisms of their antiviral actions will be further adressed as well. Finally, we will discuss the advantages and distadvantages of the use of carbon dots in the tangled battle against viral infections in order to provide valuable informations for further research and development of new virus biosensors and antiviral therapeutics.

Ultrasensitive photoelectrochemical microcystin-LR immunosensor using carboxyl-functionalized graphene oxide enhanced gold nanoclusters for signal amplification

An ultrasensitive photoelectrochemical (PEC) immunosensor based on gold nanoclusters (AuNCs) with 11-mercaptoundecanoic acid (MUA) ligands was fabricated for determination of microcystin-LR (MC-LR). The PEC immunosensor was developed by loading the monoclonal MC-LR antibody (Ab) to the MUA-AuNCs modified gold electrodes. After different measurement conditions being optimized, silver nanoparticles (AgNPs), gold nanorods (AuNRs), graphene oxide (GO) and carboxyl-functionalized graphene oxide (cGO) were introduced into MUA-AuNCs to enhance the sensing properties. The experimental result revealed that the sensitivity of PEC immunosensors was enhanced by both their photoelectrochemical properties and antibody loading properties with dependent relationship, which was different from the enhancement strategy of PEC sensors based on redox reactions. Among different hybrid nanocomposites, MUA-AuNCs/cGO not only improved the photoelectrochemical properties, but also loaded more antibodies for sensing, which resulted in best sensing performance. Thus, a universal method was proposed to enhance the sensing performance of PEC immunosensors based on impedance changes. Finally, MUA-AuNCs/cGO based PEC immunosensors exhibited a wide linear range of 0.001 nM-1000 nM with low detection limit of 0.011 pM (S/N = 3) for MC-LR determination. Meanwhile, the designed PEC immunosensors showed high selectivity, reproducibility and specificity, which provided the promising applications in aquatic environment.

Nanomaterials as Novel Cardiovascular Theranostics

Cardiovascular diseases (CVDs) are a group of conditions associated with heart and blood vessels and are considered the leading cause of death globally. Coronary heart disease, atherosclerosis, myocardial infarction represents the CVDs. Since CVDs are associated with a series of pathophysiological conditions with an alarming mortality and morbidity rate, early diagnosis and appropriate therapeutic approaches are critical for saving patients’ lives. Conventionally, diagnostic tools are employed to detect disease conditions, whereas therapeutic drug candidates are administered to mitigate diseases. However, the advent of nanotechnological platforms has revolutionized the current understanding of pathophysiology and therapeutic measures. The concept of combinatorial therapy using both diagnosis and therapeutics through a single platform is known as theranostics. Nano-based theranostics are widely used in cancer detection and treatment, as evident from pre-clinical and clinical studies. Nanotheranostics have gained considerable attention for the efficient management of CVDs. The differential physicochemical properties of engineered nanoparticles have been exploited for early diagnosis and therapy of atherosclerosis, myocardial infarction and aneurysms. Herein, we provided the information on the evolution of nano-based theranostics to detect and treat CVDs such as atherosclerosis, myocardial infarction, and angiogenesis. The review also aims to provide novel avenues on how nanotherapeutics’ trending concept could transform our conventional diagnostic and therapeutic tools in the near future.

Integrating gold nanoclusters, folic acid and reduced graphene oxide for nanosensing of glutathione based on "turn-off" fluorescence

Glutathione (GSH) is a useful biomarker in the development, diagnosis and treatment of cancer. However, most of the reported GSH biosensors are expensive, time-consuming and often require complex sample treatment, which limit its biological applications. Herein, a nanobiosensor for the detection of GSH using folic acid-functionalized reduced graphene oxide-modified BSA gold nanoclusters (FA-rGO-BSA/AuNCs) based on the fluorescence quenching interactions is presented. Firstly, a facile and optimized protocol for the fabrication of BSA/AuNCs is developed. Functionalization of rGO with folic acid is performed using EDC/NHS cross-linking reagents, and their interaction after loading with BSA/AuNCs is demonstrated. The formation of FA-rGO, BSA/AuNCs and FA-rGO-BSA/AuNCs are confirmed by the state-of-art characterization techniques. Finally, a fluorescence turn-off sensing strategy is developed using the as-synthesized FA-rGO-BSA/AuNCs for the detection of GSH. The nanobiosensor revealed an excellent sensing performance for the detection of GSH with high sensitivity and desirable selectivity over other potential interfering species. The fluorescence quenching is linearly proportional to the concentration of GSH between 0 and 1.75 µM, with a limit of detection of 0.1 µM under the physiological pH conditions (pH 7.4). Such a sensitive nanobiosensor paves the way to fabricate a "turn-on" or "turn-off" fluorescent sensor for important biomarkers in cancer cells, presenting potential nanotheranostic applications in biological detection and clinical diagnosis.

Introducing visible-light sensitivity into photocatalytic CeO2 nanoparticles by hybrid particle preparation exploiting plasmonic properties of gold: enhanced photoelectrocatalysis exemplified for hydrogen peroxide sensing

In this report we combine the catalytic properties of CeO₂ nanoparticles with their transduction ability for photoelectrochemical sensing. This study highlights the usage of CeO₂ providing catalytic activity towards H₂O₂, but only with a limited excitation range in the UV for the construction of a sensing system. In order to improve the photoelectrocatalysis of CeO₂ nanoparticles by extending their excitation to visible light, Au/CeO₂ core/shell hybrid nanoparticles have been synthesized. The hybrid nanoparticles are fixed on electrodes, allowing for the generation of photocurrents, the direction of which can be controlled by the electrode potential (without bias). The application of the hybrid nanoparticles results in an enhanced photocurrent amplitude under white light illumination as compared to the pure CeO₂ nanoparticles. Wavelength-dependent measurements confirm the participation of the Au core in the signal transduction. This can be explained by improved charge carrier generation within the hybrid particles. Thus, by using a plasmonic element the photoelectochemical response of a catalytic nanoparticle (i.e. CeO₂) has been spectrally extended. The effect can be exploited for sensorial hydrogen peroxide detection. Here higher photocatalytic current responses have been found for the hybrid particles fixed to gold electrodes although the catalytic reduction has been comparable for both types of nanoparticles. Thus, it can be demonstrated that Au/CeO₂ core-shell nanoparticles allow the utilization of visible light for photoelectrochemical hydrogen peroxide (H₂O₂) detection with improved sensitivity under white light illumination or application of such particles with only visible light excitation, which is not possible for pure CeO₂. With help of the layer-by-layer (LbL) technique for nanoparticle immobilization, the electrode response can be adjusted and with a 5 layers electrode a low detection limit of about 3 μM H₂O₂ with a linear detection range up to 2000 μM is obtained.

High-efficiency artificial enzyme cascade bio-platform based on MOF-derived bimetal nanocomposite for biosensing

In this paper, a high-performance enzyme cascade bio-platform has been developed for biosensing by combining MOFs-based nanozyme and natural enzymes. Firstly, a novel porous mixed bi-metal oxide (MnCo₂O₄) derived from MOF with rod-like nanostructures was synthesized. Based on this, the nanozyme of bovine serum albumin-Pt nanoparticles@mesoporous MnCo₂O₄ (BSA-PtNP@MnCo₂O₄) was successfully synthesized and used to construct enzyme cascade bio-platform. The nanozyme had unique physicochemical surface properties and hierarchical structure. Due to the synergistic effect of protein, bimetal oxide and PtNP, the nanozyme presented excellent dual enzyme activity. On the one hand, BSA-PtNP@MnCo₂O₄ can be used as nanozyme with oxidase activity to achieve superior detection of glutathione with detection limit of 0.42 μM. On the other hand, BSA- PtNP@MnCo₂O₄ can also be used both as the nanozyme with great peroxidase activity and as a scaffold for immobilization of glucose oxidase (GOx), guiding an organized high-efficiency enzyme cascade bio-platform. The platform combined advantages of nanozyme and natural enzyme, and provided excellent glucose detection with the detection limit of 8.1 μM. The tandem catalytic system not only broadened the application of nanozyme in natural enzyme catalysis, but also provided a simple, efficient and organized enzyme cascade bio-platform for biosensing and other applications.

Silver nanoclusters and carbon dots based light-addressable sensors for multichannel detections of dopamine and glutathione and its applications in probing of parkinson's diseases

Parkinson's disease (PD) is a common neurological disease caused by nerve cells degradation which leads to extremely low level of dopamine (DA) in patients. Therefore, ultrasensitive DA detection is particularly important for the assessment and treatment of Parkinson's patients. In this research, photoelectrochemical (PEC) sensors based on Ag₄₄(SR)₃₀ nanoclusters (AgNCs) with 5-mercapto-2-nitrobenzoic acid (MNBA) ligands were first developed for ultrasensitive and selective detection of DA. Then, hybrid nanomaterials by introducing graphene oxide (GO) and silver nanoparticles (AgNPs) into AgNCs were used to enhance sensing properties. AgNCs/AgNPs/GO based PEC sensors achieved high sensitivity (7.476 nA/μM) and low limit of detection (LOD, S/N = 3, 53 nM) in the linear range 0.16-6 μM DA concentration. Besides DA, PD causes the concentration change of other analytes, such as glutathione (GSH). Multichannel detections of different analytes can provide more information in studying PD. Therefore, carbon dots (CDs) based PEC sensors were designed and achieved high sensing performances on GSH detection. Then, AgNCs/AgNPs/GO and CDs based PEC sensors were combined and extended into light-addressable sensors for multichannel detections of DA and GSH. Algorithms were used to solve interference problems to improve the measurement accuracy of DA and GSH in complex solution. Finally, PD biological model samples from mice were measured by light-addressable sensors. The relationships between the DA and GSH concentration and the PD stage were proved. Our designed light-addressable sensors exhibited advantages of multichannel detection, high sensitivity, fast response and so on. In the future, it can be expanded to detect more biological molecules to provide more information on studying PD.

Photonic Carbon Dots as an Emerging Nanoagent for Biomedical and Healthcare Applications

As a class of carbon-based nanomaterials, carbon dots (CDs) have attracted enormous attention because of their tunable optical and physicochemical properties, such as absorptivity and photoluminescence from ultraviolet to near-infrared, high photostability, biocompatibility, and aqueous dispersity. These characteristics make CDs a promising alternative photonic nanoagent to conventional fluorophores in disease diagnosis, treatment, and healthcare managements. This review describes the fundamental photophysical properties of CDs and highlights their recent applications to bioimaging, photomedicine (e.g., photodynamic/photothermal therapies), biosensors, and healthcare devices. We discuss current challenges and future prospects of photonic CDs to give an insight into developing vibrant fields of CD-based biomedicine and healthcare.

An antibody-aptamer sandwich cathodic photoelectrochemical biosensor for the detection of progesterone

The progesterone (P4) level in body fluids can act as an indicator for early pregnancy diagnosis and offers insight into mammalian somatic function. In this work, we designed an antibody-aptamer based sandwich assay as a cathodic photoelectrochemical (PEC) biosensor for P4 detection. The composites of carbon dots and graphene oxide (CDs-GO) with favorable cathodic photocurrent response were used as photoactive materials on which the antibody (Ab) of P4 was immobilized. Meanwhile, high affinity truncated P4 aptamer was immobilized on Au-CuO-Cu₂O to act as a bioconjugate. When P4 was present, the aptamer-Au-CuO-Cu₂O bioconjugate could amplify the cathodic photocurrent of CDs-GO modified electrode through Ab-P4-aptamer interactions. Under optimum conditions, the cathodic photocurrent of the constructed PEC biosensor was found to increase linearly with P4 in a wide concentration range from 0.5 nM to 180 nM, with a low detection limit (3S/N) of 0.17 nΜ. The proposed cathodic PEC sensing platform demonstrated high selectivity, satisfying reproducibility, good stability. The sensor was successfully applied in the determination of P4 in human serum samples.

Platinum and Iridium Oxide Co-modified TiO2 Nanotubes Array Based Photoelectrochemical Sensors for Glutathione

Oriented TiO₂ nanotubes, which are fabricated by anodic oxidation method, are prospective in photoelectrochemical analysis and sensors. In this work, Pt and IrO₂ co-modified TiO₂ nanotubes array was prepared via a two-step deposition process involving the photoreductive deposition of Pt and chemical deposition of IrO₂ on the oriented TiO₂ nanotubes. Due to the improved separation of photo-generated electrons and holes, Pt-IrO₂ co-modified TiO₂ nanotubes presented significantly higher PEC activity than pure TiO₂ nanotubes or mono-modified TiO₂ nanotubes. The PEC sensitivity of Pt-IrO₂ co-modified TiO₂ nanotubes for glutathione was also monitored and good sensitivity was observed.

N, S, I co-doped carbon dots for folic acid and temperature sensing and applied to cellular imaging

The application of fluorescent carbon dots in bio-imaging has huge positive significance in the field of biomedicine. By taking this advantage, herein we prepared nitrogen, sulfur and iodine doped carbon dots (N,S,I-CDs) by a facile hydrothermal reaction using C₃N₃S₃, potassium iodate (KIO₃) and ethylenediamine (EDA), and the obtained N,S,I-CDs show bright blue fluorescence with a high fluorescence quantum yield of about 32.4%. The prepared N, S, I-CDs could interact with the folic acid (FA) with high selectivity, lead to development of a high sensitive method for the FA detection from 0.1 to 175 μM wide linear range with a detection limit of 84 nM (S/N = 3) and also applied them in U-2 OS cells imaging. Moreover, this sensor possessed a good sensitivity, linearity and reversibility in the temperature range of 10-80 °C, and successfully applied for the temperature sensing in cell HT-29 samples. This investigation illustrates that as-prepared N, S, I-CDs probe may have great potential as a high-performance platform for the accurate recognition of temperature in cells and could provide a new tool for the detection of FA in cells.

Boron and nitrogen codoped carbon dots as fluorescence sensor for Fe3+ with improved selectivity

Carbon dots (CDs) are popular as fluorescence sensors, and metal ions are typical analytes. However, CDs used as fluorescent sensors for Fe³⁺ have some interferences coming from co-existed ions. In this study, we suspect that sp³ boron atom in phenylboronic acid group will be more compatible with Fe³⁺ to form coordination bonds, thereby increasing the selectivity to Fe³⁺. Hence, we designed and synthesized boron and nitrogen codoped carbon dots (BN-CDs) for detection of Fe³⁺ via a hydrothermal method using o-phenylenediamine (OPA) and 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzylchloroformate as precursors. From the results, we found that BN-CDs had superior selectivity to Fe³⁺ in the presence of the other common interfering metal ions like Cu²⁺, Fe²⁺ and Pb²⁺. Besides, the obtained BN-CDs exhibited good water solubility, favorable photostability, excellent pH stability between pH 2-11, and strong fluorescence intensity with quantum yield up to 31.5 %. These excellent properties of carbon dots validate that our idea is feasible, and can be used for design CDs for Fe³⁺ detection. Quenching mechanism study showed the fluorescence intensity of BN-CDs could be dramatically quenched by Fe³⁺ through dynamic and static synergy process. Finally, the as prepared BN-CDs were successfully applied to the determination of Fe³⁺ in fetal bovine serum and lake water.

New insights into bioelectronic medicines: A new approach to tackle diabetic peripheral neuropathy pain in clinics

Bioelectronic medicines are a newer way to treat and diagnose the diseases associated with biological systems. All vital organs of the body are innervated, commanding brain to regulate the homeostasis functions. Bioelectronic medicines rely on implications of electrical stimulations or signals associated with the nervous system for real-time treatment. Diabetic peripheral neuropathy (DPN) is a most prevalent micro-vascular complication associated with diabetes mellitus. Complex plexus of nerves were affected in this complication with impaired function. Bioelectronic medicines are future hope for effective treatment of DPN.

A visible-light-driven photoelectrochemical molecularly imprinted sensor based on titanium dioxide nanotube arrays loaded with silver iodide nanoparticles for the sensitive detection of benzoyl peroxide

A novel ultrasensitive photoelectrochemical sensor for benzoyl peroxide (BPO) was constructed under visible light irradiation.