Detection of Few Hydrogen Peroxide Molecules Using Self-Reporting Fluorescent Nanodiamond Quantum Sensors

Effect of H2O2 Concentration on the Electrochemical H2O2 Oxidation and Reduction Reactions on the Pt/C Catalyst in Acid Solutions

Hydrogen peroxide (H2O2) oxidation reaction (HPOR) and reduction reaction (HPRR) play vital roles in various innovative H2O2-related electrochemical energy conversion systems. Understanding the interactions of H2O2 with catalyst surfaces and its impact on HPOR/HPRR activity at the working potential is essential for the further development of these H2O2-related systems. Herein, we investigate the effects of the H2O2 concentration on the HPOR/HPRR activities for Pt/C catalysts and reveal the complex influence of H2O2 on the oxygen coverage of the Pt surface at various potentials. In addition, we find that the apparent number of electrons transferred at the HPRR potential differs from its theoretical value, which is attributed to the release of unreacted hydroxyl radicals via the chemical dissociation of H2O2 at the Pt surface. These findings expand our understanding of the interactions of H2O2 and Pt/C catalysts at the electrochemical interface for HPOR and HPRR, providing valuable insights into the underlying reaction mechanisms.

Laser-assisted thermoelectric-enhanced hydrogen peroxide biosensors based on Ag2Se nanofilms for sensitive detection of bacterial pathogens

Thermoelectric (TE) materials can convert the heat produced during biochemical reactions into electrical signals, enabling the self-powered detection of biomarkers. In this work, we design and fabricate a simple Ag2Se nanofilm-based TE biosensor to precisely quantify hydrogen peroxide (H2O2) levels in liquid samples. A chemical reaction involving horseradish peroxidase, ABTS and H2O2 in the specimens produces a photothermal agent-ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) free radical, which triggers the heat fluctuations at the TE sensor through the photo-thermal effect, eventually enabling the sensing of H2O2. Consequently, the constructed sensor can achieve a detection limit of 0.26 μM by a three-leg TE device design. Further investigations suggest that the application of our TE sensor can be extended in testing H2O2 in beverages (including milk, soda water, and lemonade) and evaluating the load of bacterial pathogens relevant to dental diseases and infections including Streptococcus sanguinis and Methicillin-resistant Staphylococcus aureus with high analytical accuracy. This strategy utilizes the combination of high thermoelectric performance with chemical reactions to realize a straightforward and accurate biomarker detection method, making it suitable for applications in medical diagnostics, personalized health monitoring, and the food industry.

Highly sensitive photoluminescence sensor based on chitosan biopolymer film for determination of hydrogen peroxide

Determination of hydrogen peroxide (H2O2) is of great importance in many systems for controlling the quality of products, food safety, and medical diagnostics. In this work, a highly sensitive photoluminescence film sensor was synthesized based on chitosan (CS), polyvinyl alcohol (PVA), and terephthalic acid (TPA), in the presence of copper (II) ions for determination of hydrogen peroxide. TPA was used as a sensitive probe for detection of hydroxyl radicals produced in a photo-Fenton-like process. Several important factors that can affect the fluorescence response of the sensor were investigated, including the irradiation time, pH, and the amount of catalyst. The response of the sensor (CS/PVA-Cu-TPA) was greatly improved by UV irradiation. The structure of the film sensor was studied by FT-IR, TGA, SEM, and X-ray mapping analysis. The highest response values were observed under the optimum conditions (0.7 % w/w Cu (II) ions, 4.25 % w/w TPA, 45 min UV irradiation, and excitation at 315 nm). This method can be applied for determination of H2O2 with a limit of detection (LOD) of about 0.1 μM and limit of quantification (LOQ) of about 0.33 μM. The practical value of the highly sensitive fluorescence sensor was illustrated by its application in milk samples.

Electrochemical-Enhanced Charge State Modulation of Nitrogen-Vacancy Centers for Ultrasensitive Biodetection of MicroRNA-155

Sensitive and accurate miRNA detection is important in cancer diagnosis but remains challenging owing to the essential features of miRNAs, such as their small size, high homology, and low abundance. This work proposes a novel electrochemical (EC)-enhanced quantum sensor achieving quantitative detection of miRNA-155 with simultaneous EC sensing. Specifically, fluorescent nanodiamonds/MXene nanocomposites were synthesized and modified with dual-mode signal labels, enabling miRNA-155 concentration measurement via T1 relaxation time of nitrogen-vacancy (NV) centers and EC signals. Quantum sensing was enhanced via external voltage during the EC process, which modulated the negatively charged state of the NV centers, thereby improving the sensitivity and accuracy of miRNA-155 detection. EC sensing improved the accuracy and reliability of miRNA-155 detection while enhancing quantum sensing. The limit of detection (LOD) of the EC-enhanced quantum biosensor reached 10.0 aM, nearly 106 and 10 times lower than the reported LODs of a quantum sensor using bulk diamond and fluorescent sensors, respectively. The LOD of EC sensing was 2.6 aM, aligning with previous reports. The findings of the study indicated that quantum sensing combined with EC sensing can achieve ultrasensitive miRNA-155 detection with high accuracy and reliability, providing an advanced approach for early cancer diagnosis.

Glucose Oxidase-Coated Calcium Peroxide Nanoparticles as an Innovative Catalyst for In Situ H2O2-Releasing Hydrogels

In situ forming and hydrogen peroxide (H2O2)-releasing hydrogels have been considered as attractive matrices for various biomedical applications. Particularly, horseradish peroxidase (HRP)-catalyzed crosslinking reaction serves efficient method to create in situ forming hydrogels due to its advantageous features, such as mild reaction conditions, rapid gelation rate, tunable mechanical strength, and excellent biocompatibility. Herein, a novel HRP-crosslinked hydrogel system is reported that can produce H2O2 in situ for long-term applications, using glucose oxidase-coated calcium peroxide nanoparticles (CaO2@GOx NPs). In this system, CaO2 gradually produced H2O2 to support the HRP-mediated hydrogelation, while GOx further catalyzed the oxidation of glucose for in situ H2O2 generation. As the hydrogel is formed rapidly is expected and the H2O2 release behavior is prolonged up to 10 days. Interestingly, hydrogels formed by HRP/CaO2@GOx-mediated crosslinking reaction provided a favorable 3D microenvironment to support the viability and proliferation of fibroblasts, compared to that of hydrogels formed by either HRP/H2O2 or HRP/CaO2/GOx-mediated crosslinking reaction. Furthermore, HRP/CaO2@GOx-crosslinked hydrogel enhanced the angiogenic activities of endothelial cells, which is demonstrated by the in vitro tube formation test and in ovo chicken chorioallantoic membrane model. Therefore, HRP/CaO2@GOx-catalyzed hydrogels is suggested as potential in situ H2O2-releasing materials for a wide range of biomedical applications.

The impact of phospholipids with high transition temperature to enhance redox-sensitive liposomal doxorubicin efficacy in colon carcinoma model

In this study, we have developed a redox-sensitive (RS) liposomal doxorubicin formulation by incorporating 10,10'-diselanediylbis decanoic acid (DDA) organoselenium compound as the RS moiety. Hence, several RS liposomal formulations were prepared by using DOPE, HSPC, DDA, mPEG2000-DSPE, and cholesterol. In situ drug loading using a pH gradient and citrate complex yielded high drug to lipid ratio and encapsulation efficiency (100%) for RS liposomes. Liposomal formulations were characterized in terms of size, surface charge and morphology, drug loading, release properties, cell uptake and cytotoxicity, as well as therapeutic efficacy in BALB/c mice bearing C26 tumor cells. The formulations showed an average particle size of 200 nm with narrow size distributions (PDI < 0.3), and negative surface charges varying from -6 mV to -18.6 mV. Our study confirms that the presence of the DDA compound in liposomes is highly sensitive to hydrogen peroxide at 0.1% w/v, resulting in a significant burst release of up to 40%. The in vivo therapeutic efficacy study in BALB/c mice bearing C26 colon carcinoma confirmed the promising function of RS liposomes in the tumor microenvironment which led to a prolonged median survival time (MST). The addition of hydrogenated soy phosphatidylcholine (HSPC) with a high transition temperature (Tm: 52-53.5°C) extended the MST of our 3-component formulation of F14 (DOPE/HSPC/DDA) to 60 days in comparison to Caelyx (PEGylated liposomal Dox), which is not RS-sensitive (39 days). Overall, HSPC liposomes bearing RS-sensitive moiety enhanced therapeutic efficacy against colon cancer in vitro and in vivo. This achievement unequivocally underscores the criticality of high-TM phospholipids, particularly HSPC, in significantly enhancing liposome stability within the bloodstream. In addition, RS liposomes enable the on-demand release of drugs, leveraging the redox environment of tumor cells, thereby augmenting the efficacy of the formulation.

Unraveling Eumelanin Radical Formation by Nanodiamond Optical Relaxometry in a Living Cell

Defect centers in a nanodiamond (ND) allow the detection of tiny magnetic fields in their direct surroundings, rendering them as an emerging tool for nanoscale sensing applications. Eumelanin, an abundant pigment, plays an important role in biology and material science. Here, for the first time, we evaluate the comproportionation reaction in eumelanin by detecting and quantifying semiquinone radicals through the nitrogen-vacancy color center. A thin layer of eumelanin is polymerized on the surface of nanodiamonds (NDs), and depending on the environmental conditions, such as the local pH value, near-infrared, and ultraviolet light irradiation, the radicals form and react in situ. By combining experiments and theoretical simulations, we quantify the local number and kinetics of free radicals in the eumelanin layer. Next, the ND sensor enters the cells via endosomal vesicles. We quantify the number of radicals formed within the eumelanin layer in these acidic compartments by applying optical relaxometry measurements. In the future, we believe that the ND quantum sensor could provide valuable insights into the chemistry of eumelanin, which could contribute to the understanding and treatment of eumelanin- and melanin-related diseases.

Chemical-chemical redox cycling for improving the sensitivity of the fluorescent assay: A proof-of-concept towards DNA methylation detection

Ultrasensitive analytical methods are still urgent for the discovery of trace level biomarkers and the early clinical diagnosis of disease. In this work, an ultrasensitive universal sensing platform was constructed by integrating fluorescent assay with chemical-chemical redox cycling signal amplification strategy. Using Ru@SiO2 nanoparticles wrapped by MnO2 nanosheets (Ru@SiO2@MnO2) as fluorescent probe, the chemical-chemical redox cycling system was conducted upon ascorbic acid (AA) and tris(2-carboxyethyl)phosphine (TCEP) as reductants and MnO2 nanosheets as oxidant. The MnO2 nanosheets not only could quench the fluorescence of Ru@SiO2 nanoparticles to reduce the background, but also could serve as oxidants to react with AA, generating dehydroascorbic acid (DHA). The DHA was reduced by TCEP in turn to form AA that participated in the next cycling of chemical-chemical redox reaction. Thus, the constantly released AA from the chemical-chemical redox cycling system could massively etch MnO2 nanosheets on Ru@SiO2 surface, making the fluorescence of Ru@SiO2 nanoparticles greatly recovered. It was shown that the sensitivity of the fluorescent assay was improved almost 52 times by utilizing the chemical-chemical redox cycling signal amplification strategy. This strategy was further employed to detect DNA methylation with the aid of AA-encapsulated liposomes that were modified with 5 mC antibodies to bind with the methylated DNA captured in 96-well plate. A detection of limit down to 16.2 fM was achieved for the detection of methylated DNA. It's believed that the incorporation of chemical-chemical redox cycling signal amplification strategy into fluorescent sensing paves a new way for ultrasensitive detection of biomarkers.

Engineering a hierarchically micro-/nanostructured Si@Au-based artificial enzyme with improved accessibility of active sites for enhanced catalysis

The active site accessibility and high loading of gold nanoparticles (AuNPs) are key factors affecting the catalytic activity of supported AuNP-based catalysts. However, the preparation of supported AuNP-based catalysts with highly accessible active sites still remains a challenge. Herein, sphere-on-sphere (SoS) silica microspheres with a hierarchical structure, good dispersion and high surface density of thiol groups (10 SH nm-2) are prepared and used as a platform for the growth of high-density AuNPs. The obtained hierarchical Si@Au micro-/nanostructure consisting of 0.55 μm SoS silica microspheres and 7.3 nm AuNPs (SoS-0.55@Au-7.3) is found to show excellent peroxidase-mimicking activity (Km = 0.033 mM and Vmax = 34.6 × 10-8 M s-1) with merits of high stability and good reusability. Furthermore, the as-obtained SoS-0.55@Au-7.3-based system can sensitively detect hydrogen peroxide (H2O2) with a low detection limit of 1.6 μM and a wide linear range from 2.5 μM to 1.0 mM. The high catalytic activity, excellent stability and good reusability of SoS-0.55@Au-7.3 imply its great prospects in biosensing and biomedical analysis.

A QR code-integrated chromogenic paper strip for detection of hydrogen peroxide in aqueous samples

Hydrogen peroxide (H2O2) is commonly used as a preservative, disinfectant, bleach, and oxidizing agent. The prolonged consumption of H2O2 adulterated milk is harmful to human health when consumed in the diet. Exposure to H2O2 can lead to oxidative stress, cell damage and tissue injury. Due to the potential adverse effects, the use of hydrogen peroxide is regulated in certain applications, such as in food, water treatment plants and medical products. Several methods are available for the detection of H2O2 in various matrices. Here, a method and QR code-integrated chromogenic paper strip for the detection of H2O2 in aqueous samples has been developed. The spectrophotometric method showed an LOD and LOQ of 0.00087 ± 8.70 ×10-5% (v/v) and 0.0037 ± 0.0003% (v/v), respectively. The paper-based chromogenic strip prepared by immobilizing recognition solution onto a QR code was able to detect 0.0005% v/v of H2O2 in aqueous samples. The QR integrated chromogenic paper strip sensors can serve as a useful tool for consumers, regulatory agencies, and the food industry to assess food quality and authenticity.

Phosphate-driven H2O2 decomposition on DNA-bound bio-inspired activated carbon-based sensing platform for biological and food samples

Hydrogen peroxide (H₂O₂) is one of the most important reactive oxygen species (ROS). Increased endogenous H₂O₂ levels indicate oxidative stress and could be a potential marker of many diseases, including Alzheimer's, cardiovascular diseases, and diabetes. However, consuming H₂O_2-incorporated food has adverse effects on humans and is a serious health concern. We used salmon testes DNA with bio-inspired activated carbon (AC) as an electrocatalyst for developing a novel H₂O₂ sensor. The phosphate backbone of DNA contains negatively charged oxygen groups that specifically attract protons from H₂O₂ reduction. We observed a linearity range of 0.01-250.0 μM in the H₂O₂ reduction peak current with a detection limit of 2.5 and 45.7 nM for chronoamperometric and differential pulse voltammetric studies. High biocompatibility of the sensor was achieved by the DNA, facilitating endogenous H₂O₂ detection. Moreover, this non-enzymatic sensor could also help in the rapid screening of H₂O₂-contaminated foods.

Single-atom catalysts with peroxidase-like activity boost gel-sol transition-based biosensing

Gel-sol transition-based biosensors are a promising and popular alternative for portable, cost-effective, and user-friendly point-of-care testing (POCT). However, the improvement of sensitivity and practicability is highly demanded. In this work, a Fe-NC single-atom catalyst (SAC) is successfully synthesized and used as a signal amplification element for highly sensitive gel-sol transition-based biosensing. The Fe-NC SAC owns excellent peroxidase-like activity of 188 U/mg due to its definite atomically active centers and maximum atomic utilization of active metal atoms. As a proof-of-concept, the Fe-NC SAC is uniformly encapsulated in gelatin hydrogel to obtain a hydrogel sensor that allows colorimetric detection of trypsin based on gel-sol transition. The gelatin hydrogel network collapses derived from the hydrolysis by trypsin, and thereby the released Fe-NC SAC leads to the colorimetric sensing process. The designed hydrogel sensor offers a low detection limit of 1 ng/mL with a range from 1 to 100 ng/mL toward trypsin detection, exhibiting excellent selectivity and sensitivity, and well-performed practical detection in human serum. This work offers a successful paradigm for designing a promising SACs-related detection strategy and paves a new way to develop high-performance gel-sol transition-based sensors and various POCT applications.

Synthesis of nitrogen mustard-based fluorophores for cell imaging and cytotoxicity studies

Nitrogen mustards are important alkylating anticancer drugs used for neoplasms treatment. However, little research about the integration of luminophore into nitrogen mustard-based compounds for both imaging and therapeutic application was reported. In this study, we report a series of novel nitrogen mustard-containing 1-furyl-2-en-1-one and 1-thienyl-2-en-1-one derivatives as intramolecular charge transfer-based luminophore for research in both imaging subcellular localization and antiproliferation toward lung cancer cells. The target products were prepared by Knoevenagel condensation and characterized by nuclear magnetic resonance and high-resolution mass spectrometer. The absorption and fluorescence studies were carried out by ultraviolet-visible and fluorescence spectrophotometers, respectively. Cell morphology was observed under an inverted microscope. Cytotoxicity test was detected by MTT assay. Cellular localization was observed by a confocal laser scanning microscope. Colony formation ability was carried out by colony formation assay. Cell migration ability was detected by transwell migration assay. Differences between the two groups were analyzed by two-tailed Student's t-test. The difference with P < 0.05 (*) was considered statistically significant. The compounds were synthesized in high yield. The λmax and Stokes shift of these compounds reach up to 567 and 150 nm, respectively. These compounds exhibited good antiproliferative activity against lung cancer cells, with compound 3h exhibiting the best IC50 of 13.1 ± 2.7 μM. Furthermore, the selected compound 3h is located preferentially in lysosomes and a small amount in nuclei, effectively inhibiting cell colony formation and migration abilities toward A549 cells. These findings suggested that nitrogen mustard-based fluorophores might be a potential effective chemotherapeutic agent in lung cancer therapy.