Exploration of Nanoparticle-Mediated Photothermal Effect of TMB-H2O2 Colorimetric System and Its Application in a Visual Quantitative Photothermal Immunoassay

Construction of a novel Au@Os mediated TMB-H2O2 platform with dual-signal output for rapid and accurate detection of ziram in food

The 3,3',5,5'-tetramethylbenzidine-H2O2 (TMB-H2O2) platform has gained widespread use for rapid detection of various analytes in foods. However, the existing TMB-H2O2 platforms suffer from limited accuracy, as their signal output is confined to the visible region, which is prone to interference from various food colorants in real samples. To address this challenge, a novel Au@Os-mediated TMB-H2O2 platform is developed for both rapid and accurate detection of analytes in foods. The prepared Au@Os NPs exhibit remarkable peroxidase-like activity, making the platform display dual absorption peaks in visible and near-infrared (NIR) regions, respectively. This Au@Os-mediated TMB-H2O2 platform exhibited three linear ranges across different concentrations of ziram from 1-100, 150-600, and 800-2000 nM with limit of detection (LOD) 7.9 nM and limit of quantification (LOQ) 24.15 nM respectively. Further, the Au@Os-mediated TMB-H2O2 platform was also used for rapid and accurate detection of ziram in real food samples like apple, tomato, and black tea.

Chemiluminescent/photothermal dual-mode lateral flow immunoassay based on CoFe PBAs/WS2 nanozyme for rapid and highly sensitive point-of-care testing of gentamicin

Serious adverse drug reactions of gentamicin (GM) significantly limit its clinical use, thus there is an urgent demand to develop reliable strategies to detect its concentration. In this study, we have developed a novel highly sensitive and portable lateral flow immunoassay (LFIA) based on CoFe PBAs/WS2 nanozyme mediated chemiluminescence (CL) and photothermal (PT) dual-mode POCT biosensor for the detection of GM, which successfully combines sensitive laboratory analyses with portable in situ analyses in the field. In this proof-of-principle work, the dynamic detection ranges of CL-LFIA and PT-LFIA mode were 1 pg mL-1 to 100 ng mL-1 and 50 pg mL-1 to 100 ng mL-1 with the limits of detection of 0.33 and 16.67 pg mL-1, respectively. The whole detection of CL-LFIA and PT-LFIA could be completed within 15 min and 30 min, respectively. The recoveries of GM spiked into complex matrices including milk, urine, and serum for CL-LFIA and PT-LFIA were 90.94%-109.74% and 94.49%-109.31%, respectively, indicating the reliability and applicability of the dual-mode LFIA in real samples. The dual-mode POCT biosensor could effectively overcome the false problems with improving accuracy and sensitivity, enabling user to precisely detect GM by laboratory analysis or on-site analysis depending on the source condition. Due to the complementary properties of CL-LFIA and PT-LFIA, the developed POCT biosensor can effectively ensure high-performance detection, showing the potential application of accurately detecting drug concentration in clinical practice.

A Nanoreactor Based on Metal-Organic Frameworks With Triple Synergistic Therapy for Hepatocellular Carcinoma

The transformation of monotherapy into multimodal combined targeted therapy to fully exploit synergistic efficacy is of increasing interest in tumor treatment. In this work, a novel nanodrug-carrying platform based on iron-based MOFs, which is loaded with doxorubicin hydrochloride (DOX), dihydroartemisinin (DHA), and glucose oxidase (GOx), and concurrently covalently linked to the photosensitizer 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP) in polydopamine (PDA)-encapsulated MIL-101(Fe) (denoted as MIL-101(Fe)-DOX-DHA@TCPP/GOx@PDA, MDDTG@P), is successfully developed. Upon entering the tumor microenvironment, MDDTG@P catalyzes the hydrogen peroxide (H2O2) into hydroxyl radicals (·OH) and depletes glutathione (GSH); thus, exerting the role of chemodynamic therapy (CDT). The reduced Fe2+ can also activate DHA, further expanding CDT and promoting tumor cell apoptosis. The introduced GOx will rapidly consume glucose and oxygen (O2) in the tumor; while, replenishing H2O2 for Fenton reaction, starving the cancer cells; and thus, realizing starvation and chemodynamic therapy. In addition, the covalent linkage of TCPP endows MDDTG@P with good photodynamic therapeutic (PDT) properties. Therefore, this study develops a nanocarrier platform for triple synergistic chemodynamic/photodynamic/starvation therapy, which has promising applications in the efficient treatment of tumors.

A paper-in-polymer-pond (PiPP) hybrid microfluidic microplate for multiplexed ultrasensitive detection of cancer biomarkers

Conventional affinity-based colorimetric enzyme-linked immunosorbent assay (ELISA) is one of the most widely used methods for the detection of biomarkers. However, rapid point-of-care (POC) detection of multiple cancer biomarkers by conventional ELISA is limited by long incubation time, large reagent volume, and costly instrumentation along with low sensitivity due to the nature of colorimetric methods. Herein, we have developed a reusable and cost-effective paper-in-polymer-pond (PiPP) hybrid microfluidic microplate for ultrasensitive and high-throughput multiplexed detection of disease biomarkers within an hour without using specialized instruments. A piece of pre-patterned chromatography paper placed in the PMMA polymer pond facilitates rapid protein immobilization to avoid intricate surface modifications of polymer and can be changed with a fresh paper layer to reuse the device. Reagents can be simply delivered from the top PMMA layer to multiple microwells in the middle PMMA layer via flow-through microwells, thereby increasing the efficiency of washing and avoiding repeated manual pipetting or costly robots. Quantitative colorimetric analysis was achieved by calculating the brightness of images scanned by an office scanner or a smartphone camera. Sandwich-type immunoassay was performed in the PiPP hybrid device after the optimization of multiple assay conditions. Limits of detection of 0.32 ng mL-1 for carcinoembryonic antigen (CEA) and 0.20 ng mL-1 for prostate-specific antigen (PSA) were obtained, which were about 10-fold better than those of commercial ELISA kits. We envisage that this simple but versatile hybrid device can have broad applications in various bioassays in resource-limited settings.

Overview of the Design and Application of Photothermal Immunoassays

Developing powerful immunoassays for sensitive and real-time detection of targets has always been a challenging task. Due to their advantages of direct readout, controllable sensing, and low background interference, photothermal immunoassays have become a type of new technology that can be used for various applications such as disease diagnosis, environmental monitoring, and food safety. By modification with antibodies, photothermal materials can induce temperature changes by converting light energy into heat, thereby reporting specific target recognition events. This article reviews the design and application of photothermal immunoassays based on different photothermal materials, including noble metal nanomaterials, carbon-based nanomaterials, two-dimensional nanomaterials, metal oxide and sulfide nanomaterials, Prussian blue nanoparticles, small organic molecules, polymers, etc. It pays special attention to the role of photothermal materials and the working principle of various immunoassays. Additionally, the challenges and prospects for future development of photothermal immunoassays are briefly discussed.

Multivalent Pt/Ti3C2Tx Nanocomposite-Based Immunochromatographic Sensor for Colorimetric/Temperature/Pressure Trimodal Detection

Multimodal immunochromatographic sensors (ICSs) have acquired extensive attention since they not only provide reliable results by comparing the different output signals but also flexibly respond to various application environments. Herein, an ICS with triple signal outputs including colorimetry, temperature, and pressure was developed for sensitive detection of chlorothalonil. The multivalent Pt/Ti3C2Tx nanoparticles as signal tags were facilely synthesized by loading PtNPs onto single-layer Ti3C2Tx nanosheets with high surface area. The acquired Pt/Ti3C2TxNPs accelerated the rate-limiting step of the aerogenesis reaction of H2O2 for producing intensive pressure signals due to their significant catalase-mimic activity. Meanwhile, they showed desirable photothermal conversion efficiency in the near-infrared region for producing significant temperature signals. Furthermore, their deep color also allowed facile colorimetry by using the naked eye. Based on a competitive immunoassay, chlorothalonil was detected as a model analyte on this trimodal ICS platform. The detection limits for pressure, temperature, and colorimetric modes were 0.04, 0.09, and 5 ng mL-1, respectively. The recoveries for detecting chlorothalonil supplemented in Astragalus and Honeysuckle with pressure mode were 84.0-110% and 108-114%, respectively. Therefore, the ICS presented a portable, sensitive, accurate, and flexible multimodal strategy suitable for point-of-care testing.

Construction of a Three-Dimensional-Printed Immunosensing Platform Based on Smartphone Photothermal Signal Integration

The combination of the photothermal effect and immunoassay serves as a potent tool for crafting cost-effective and user-friendly biosensing systems. To ensure efficient light-to-heat conversion, we integrated three-dimensional-printed (3D printed) technology to devise a novel design. This design functions as the structural support for both the cell phone and laser probe, as well as a means for sample handling. The main body features a three-way cavity structure, securing the test sample at a fixed position to maintain consistent light distance and angle, thereby minimizing testing errors. Card slot insert facilitates precise sample positioning to ensure the adequacy of receiving light. The sample holder's wide front and narrow back design enables the accommodation of fixed samples while providing a broad field of view, with intervals therein effectively preventing cascading heat. Our design employs MB@MOF235 (methylene blue adsorbed by iron terephthalate) as the photothermal reagent, successfully enabling the detection of α-fetoprotein (AFP). The detection range spans from 0.01 to 50 ng/mL, with a lower detection limit (LOD) of 0.032 pg/mL. The detection method, combining simplicity, portability, and visualization, offers a reliable reference for furthering precision medicine toward personalized medicine. Meanwhile, to verify the method's accuracy electrochemical testing was conducted to support the proof using the electro-oxidizing activity of MB.

A sensitive Ag+-mediated magnetic relaxation and colorimetry dual-mode sensing platform

To address the relatively low sensitivity of current redox reagent-mediated magnetic relaxation sensing methods, we present a novel Ag+-mediated magnetic sensing platform that enhances the sensitivity by three orders of magnitude. The new sensing platform is based on Ag+-catalyzed oxidation of Mn2+ to KMnO4, accompanied by a distinct color change, which facilitates colorimetric detection. In the case of insufficient Ag+ ions, MnO2 is an additional oxidation product and the KMnO4/MnO2 ratio is dependent on the concentration of Ag+. When combined with a specific quantity of reducing agent, both KMnO4 and MnO2 are reduced to Mn2+ with a large relaxivity, and the concentration of Mn2+ in the resultant solution inversely correlates with the amount of KMnO4 since KMnO4 consumes more reductant during reduction. Consequently, the transverse relaxation rate of the solution exhibits a negative correlation with the Ag+ concentration. Thus, by coupling this Ag+-mediated Mn2+ to KMnO4 transformation with reactions that modulate Ag+ concentration, a dual-mode sensing platform for magnetic relaxation and colorimetry can be realized. Herein, we take H2O2 as an example to verify the detection performance of this sensing platform since H2O2 can oxidize Ag0 in Ag@Fe3O4 nanoparticles to Ag+. Experimental findings demonstrate detection limits of 10 nM and 20 nM for the magnetic relaxation and colorimetry modes, respectively, affirming the excellent sensitivity and the potential practical application of this strategy.

Rapid photothermal assay for ultrasensitive point-of-care detection of tumor markers based on a filter membrane

An ultrasensitive photothermal assay was designed for point-of-care testing (POCT) of tumor markers based on a filter membrane. Firstly, Cu2-xSe was successfully encapsulated in liposome spheres with biotin on the surface and connected to carcinoembryonic antigen (CEA) aptamer with 3'end modified biotin by streptavidin. Secondly, the CEA antibody was successfully modified on the surface of the nitrocellulose membrane through simple incubation. Finally, the assay process was completed using a disposable syringe, and the temperature was recorded using a handheld infrared temperature detector. In the range 0-50 ng mL-1, the temperature change of the nitrocellulose membrane has a strong linear relationship with CEA concentration, and the detection limit is 0.097 ng mL-1. It is worth noting that the entire testing process can be easily performed in 10 min, much shorter than traditional clinical methods. In addition, this method was successfully applied to the quantitative determination of CEA levels in human serum samples with a recovery of 96.2-103.3%. This rapid assay can be performed by "one suction and one push" through a disposable syringe, which is simple to operate, and the excellent sensitivity reveals the great potential of the proposed strategy in the POCT of tumor biomarkers.

A Programmable Microfluidic Paper-Based Analytical Device for Simultaneous Colorimetric and Photothermal Visual Sensing of Multiple Enzyme Activities

New strategies for the simultaneous and portable detection of multiple enzyme activities are highly desirable for clinical diagnosis and home care. However, the methods developed thus far generally suffer from high costs, cumbersome procedures, and heavy reliance on large-scale instruments. To satisfy the actual requirements of rapid, accurate, and on-site detection of multiple enzyme activities, we report herein a smartphone-assisted programmable microfluidic paper-based analytical device (μPAD) that utilizes colorimetric and photothermal signals for simultaneous, accurate, and visual quantitative detection of alkaline phosphatase (ALP) and butyrylcholinesterase (BChE). Specifically, the operation of this μPAD sensing platform is based on two sequential steps. Cobalt-doped mesoporous cerium oxide (Co-m-CeO2) with remarkable peroxidase-like activities under neutral conditions first catalytically decomposes H2O2 for effectively converting colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidized TMB (oxTMB). The subsequent addition of ALP or BChE to their respective substrates produces a reducing substance that can somewhat inhibit the oxTMB transformation for compromised colorimetric and photothermal signals of oxTMB. Notably, these two-step bioenzyme-nanozyme cascade reactions strongly support the straightforward and excellent processability of this platform, which exhibit lower detection limits for ALP and BChE with a detection limit for BChE an order of magnitude lower than those of the other reported paper-based detection methods. The practicability and efficiency of this platform are further demonstrated through the analysis of clinical serum samples. This innovative platform exhibits great potential as a facile yet robust approach for simultaneous, accurate, and on-site visual detection of multiple enzyme activities in authentic samples.

Facile Estimation of Surface Oxygen Vacancies in Co3O4 Catalysts with a Colorimetric Method

Oxygen vacancy (Ov) is known to act as an active center of the metal oxide. Quantification of surface Ov is vital for understanding the quantitative structure-activity relationship. Facile quantification characterization of surface Ov is highly desirable but still challenging. In this study, we presented a simple colorimetric method for rapidly quantifying surface Ov. As an example of metal oxide nanoparticles, Co3O4 was used to catalyze the 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2 colorimetric reaction. It was found that the absorbance of the TMB-H2O2 system was dependent on the surface Ov amount in Co3O4. The investigation of the mechanism showed that the Ov-dependent absorbance would be attributed to the activity of surface Ov to easily adsorb and dissociate H2O2 into a hydroxyl radical (•OH). The absorbance signal of the TMB-H2O2 system acted as a probe to estimate the surface Ov. This colorimetric measurement could be completed in less than 20 min. The Ov concentrations obtained by the proposed colorimetric method matched well with those obtained by X-ray photoelectron spectroscopy. This method does not require any complex operation and expensive equipment and can be performed in any ordinary chemical laboratory. So, this colorimetric method is expected to become an alternative approach for quantifying the surface Ov in metal oxide nanoparticles. This method will provide essential insights into the rational design and application of Ov.

A photothermal aptasensor based on rolling circle amplification-enriched DNAzyme for portable detection of ochratoxin A in grape juice

Aptasensors for detection of ochratoxin A (OTA) have been extensively studied, but the majority of them require costly and large-scale equipment as signal readers. Herein, a photothermal aptasensor capable of portable detection of OTA through a thermometer was developed on basis of aptamer structural switching and rolling circle amplification (RCA)-enriched DNAzyme. Oligonucleotides and alkaline phosphatase (ALP) modified magnetic beads were prepared. The binding of aptamers to OTA led to the release of ALP labeled complementary DNA. After magnetic separation, ALP catalyzed the padlock dephosphorylation, inhibiting the subsequent RCA reaction. This process converted the OTA concentration into the amount of the photothermal reagent oxTMB produced from the catalytic reaction induced by RCA-enriched DNAzyme. Under the optimal conditions, the detection limit (LOD) of this aptasensor was 2.28 nM in a clean buffer, while the LOD reached 2.43 nM in 2 % grape juice. The good performance of the photothermal aptasensor makes it possible to measure OTA pollution in low resource environments.

Fluorophore and nanozyme-functionalized DNA walking: A dual-mode DNA logic biocomputing platform for microRNA sensing in clinical samples

Inspired by the programmability and modifiability of nucleic acids, point-of-care (POC) diagnostics for nucleic acid target detection is evolving to become more diversified and intelligent. In this study, we introduce a fluorescent and photothermal dual-mode logic biosensing platform that integrates catalytic hairpin assembly (CHA), toehold-mediated stand displacement reaction (SDR) and a DNA walking machine. Dual identification and signal reporting modules are incorporated into DNA circuits, orchestrated by an AND Boolean logic gate operator and magnetic beads (MBs). In the presence of bispecific microRNAs (miRNAs), the AND logic gate activates, driving the DNA walking machine, and facilitating the collection of hairpin DNA stands modified with FAM fluorescent group and CeO2@Au nanoparticles. The CeO2@Au nanoparticles, served as a nanozyme, can oxidize TMB into oxidation TMB (TMBox), enabling a near-infrared (NIR) laser-driven photothermal effect following the magnetic separation of MBs. This versatile platform was employed to differentiate between plasma samples from breast cancer patients, lung cancer patients, and healthy donors. The thermometer-readout transducers, derived from the CeO2@Au@DNA complexes, provided reliable results, further corroborated by fluorescence assays, enhancing the confidence in the diagnostics compared to singular detection method. The dual-mode logic biosensor can be easily customized to various nucleic acid biomarkers and other POC signal readout modalities by adjusting recognition sequences and modification strategies, heralding a promising future in the development of intelligent, flexible diagnostics for POC testing.

Multifunctional 2D hemin-bridged MOF for the efficient removal and dual-mode detection of organophosphorus pesticides

The high-residual and bioaccumulation property of organophosphorus pesticides (OPs) creates enormous risks towards the ecological environment and human health, promoting the research for smart adsorbents and detection methods. Herein, 2D hemin-bridged MOF nanozyme (2D-ZHM) was fabricated and applied to the efficient removal and ultrasensitive dual-mode aptasensing of OPs. On the one hand, the prepared 2D-ZHM contained Zr-OH groups with high affinity for phosphate groups, endowing it with selective recognition and high adsorption capacity for OPs (285.7 mg g-1 for glyphosate). On the other hand, the enhanced peroxidase-mimicking biocatalytic property of 2D-ZHM allowed rapid H2O2-directed transformation of 3,3',5,5'-tetramethylbenzidine to oxidic product, producing detectable colorimetric or photothermal signals. Using aptamers of specific recognition capacity, the rapid quantification of two typical OPs, glyphosate and omethoate, was realized with remarkable sensitivity and selectivity. The limit of detections (LODs) of glyphosate were 0.004 nM and 0.02 nM for colorimetric and photothermal methods, respectively, and the LODs of omethoate were 0.005 nM and 0.04 nM for colorimetric and photothermal methods, respectively. The constructed dual-mode aptasensing platform exhibited outstanding performance for monitoring OPs in water and fruit samples. This work provides a novel pathway to develop MOF-based artificial peroxidase and integrated platform for pollutant removal and multi-mode aptasensing.

Realizing Ultrasensitive and Accurate Point-of-Care Profiling for ATP with a Triple-Mode Strategy Based on the ATP-Induced Reassembly of a Copper Coordination Polymer Nanoflower

New strategies for accurate and reliable detection of adenosine triphosphate (ATP) with portable devices are significant for biochemical analysis, while most recently reported approaches cannot satisfy the detection accuracy and independent of large instruments simultaneously, which are unsuitable for fast, simple, and on-site ATP monitoring. Herein, a unique, convenient, and label-free point-of-care sensing strategy based on novel copper coordination polymer nanoflowers (CuCPNFs) was fabricated for multimode (UV-vis, photothermal, and RGB values) onsite ATP determination with high selectivity, sensitivity, and accuracy. The resulting CuCPNFs with a 3D hierarchical structure exhibit the ATP-triggered decomposition behavior because the competitive coordination between ATP and the copper ions of CuCPNFs can result in the formation of ATP-Cu, which reveals preeminent peroxidase mimics activity and can accelerate the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) to form oxTMB. During this process, the detection system displayed not only color changes but also a strong NIR laser-driven photothermal effect. Thus, the photothermal and color signal variations are easily monitored by a portable thermometer and a smartphone. This multimode point-of-care platform can meet the requirements of onsite, without bulky equipment, accuracy, and reliability all at once, greatly enhancing its application in practice and paving a new way in ATP analysis.

NIR-II-Absorbing TMB Derivative for 1064 nm-Excited Photothermal Immunoassay

Materials exhibiting strong absorption in the NIR-II region are appealing for photothermal conversion-based imaging, diagnosis, and therapy, due to better thermal effect and decreased absorption of water in such a region. 3,3',5,5'-Tetramethylbenzidine (TMB), the typical substrate in ELISA, has been explored in photothermal immunoassay, since its oxidation product (oxTMB) is photothermally active in the NIR region. However, its absorption at 1064 nm (the most often used laser wavelength in photothermal studies) is not appreciable, thus limiting the assay sensitivity. Here, we proposed a derivative of TMB (3,3'-dimethoxy-5,5'-dimethylbenzidine, 2-OCH3) bearing higher NIR-II absorption for 1064 nm-excited photothermal immunoassay. Since electron-donating groups can help decrease the energy gap of molecules (here -CH3 → -OCH3), the oxidation product of 2-OCH3 exhibited substantially red-shifted absorption as compared with oxTMB, leading to a more than twofold higher absorption coefficient at 1064 nm. As a result, 2-OCH3 showed enhanced sensitivity over TMB in a photothermal immunoassay (PTIA), yielding a limit of detection (LOD) of 0.1 ng/mL for prostate-specific antigen (PSA). The feasibility of 2-OCH3-based PTIA for diagnosis was further validated by analyzing PSA in 61 serum samples. Considering its superior photothermal performance, 2-OCH3 can be explored for a broad range of photothermal applications.

Using the Photo-Piezoelectric Effect of AuPt@BaTiO3 Oxidase Mimetics for Colorimetric Detection of GSH in Serum

Nanozymes possess major advantages in catalysis and biosensing compared with natural nanozymes. In this study, the AuPt@BaTiO3 bimetallic alloy Schottky junction is prepared to act as oxidase mimetics, and its photo-piezoelectric effect is investigated. The synergy between the photo-piezoelectric effect and the local surface plasmon resonance enhances the directional migration and separation of photogenerated electrons, as well as hot electrons induced by the AuPt bimetallic alloy. This synergy significantly improves the oxidase-like activity. A GSH colorimetric detection platform is developed based on this fading principle. Leveraging the photo-piezoelectric effect allows for highly sensitive detection with a low detection limit (0.225 μM) and reduces the detection time from 10 min to 3 min. The high recovery rate (ranging from 99.91% to 101.8%) in actual serum detection suggests promising potential for practical applications. The development of bimetallic alloy heterojunctions presents new opportunities for creating efficient nanozymes.

Multiparametric modulation of magnetic transduction for biomolecular sensing in liquids

The recent COVID19 pandemic has remarkably boosted the research on in vitro diagnosis assays to detect biomarkers in biological fluids. Specificity and sensitivity are mandatory for diagnostic kits aiming to reach clinical stages. Whilst the modulation of sensitivity can significantly improve the detection of biomarkers in liquids, this has been scarcely explored. Here, we report on the proof of concept and parametrization of a novel biosensing methodology based on the changes of AC magnetic hysteresis areas observed for magnetic nanoparticles following biomolecular recognition in liquids. Several parameters are shown to significantly modulate the transducing capacity of magnetic nanoparticles to detect analytes dispersed in saline buffer at concentrations of clinical relevance. Magnetic nanoparticles were bio-conjugated with an engineered recognition peptide as a receptor. Analytes are engineered tetratricopeptide binding domains fused to the fluorescent protein whose dimerization state allows mono- or divalent variants. Our results unveil that the number of receptors per particle, analyte valency and concentration, nanoparticle composition and concentration, and field conditions play a key role in the formation of assemblies driven by biomolecular recognition. Consequently, all these parameters modulate the nanoparticle transduction capacity. Our study provides essential insights into the potential of AC magnetometry for customizing biomarker detection in liquids.

Gold nanoparticle-mediated fluorescence immunoassay for rapid and sensitive detection of Ochratoxin A

In this work, a fluorescence immunoassay based on horseradish peroxidase-labeled IgG (HRP-IgG)-modified gold nanoparticle (AuNP@HRP-IgG) probe was established for detection of ochratoxin A (OTA). Through the catalysis of HRP, the dopamine (DA) and 1,5-dihydroxynaphthalene (DHA) can rapidly generate azamonardine fluorescence compound (AFC) with intense yellow fluorescence. Large amounts of AFC can be formed within 4 min, which led to fluorescence enhancement at 545 nm. This new method displayed high sensitivity with a limit of detection (LOD) of 0.18 ng/mL and a linear range of 0.78-200 ng/mL for OTA. Meanwhile, the recoveries of OTA in corn samples were 101.41% - 113.45%. Due to the universality of the probe and the rapidity of signal output, the fluorescence immunoassay allowed rapid and sensitive detection of targets.

Sensitization Strategies of Lateral Flow Immunochromatography for Gold Modified Nanomaterials in Biosensor Development

Gold nanomaterials have become very attractive nanomaterials for biomedical research due to their unique physical and chemical properties, including size dependent optical, magnetic and catalytic properties, surface plasmon resonance (SPR), biological affinity and structural suitability. The performance of biosensing and biodiagnosis can be significantly improved in sensitivity, specificity, speed, contrast, resolution and so on by utilizing multiple optical properties of different gold nanostructures. Lateral flow immunochromatographic assay (LFIA) based on gold nanoparticles (GNPs) has the advantages of simple, fast operation, stable technology, and low cost, making it one of the most widely used in vitro diagnostics (IVDs). However, the traditional colloidal gold (CG)-based LFIA can only achieve qualitative or semi-quantitative detection, and its low detection sensitivity cannot meet the current detection needs. Due to the strong dependence of the optical properties of gold nanomaterials on their shape and surface properties, gold-based nanomaterial modification has brought new possibilities to the IVDs: people have attempted to change the morphology and size of gold nanomaterials themselves or hybrid with other elements for application in LFIA. In this paper, many well-designed plasmonic gold nanostructures for further improving the sensitivity and signal output stability of LFIA have been summarized. In addition, some opportunities and challenges that gold-based LFIA may encounter at present or in the future are also mentioned in this paper. In summary, this paper will demonstrate some feasible strategies for the manufacture of potential gold-based nanobiosensors of post of care testing (POCT) for faster detection and more accurate disease diagnosis.

A colorimetric, photothermal, and fluorescent triple-mode CRISPR/cas biosensor for drug-resistance bacteria detection

A multimodal analytical strategy utilizing different modalities to cross-validate each other, can effectively minimize false positives or negatives and ensure the accuracy of detection results. Herein, we establish a colorimetric, photothermal, and fluorescent triple modal CRISPR/Cas12a detection platform (CPF-CRISPR). An MNPs-ssDNA-HRP signal probe is designed to act as a substrate to trigger three signal outputs. In the presence of the DNA target, MNPs-ssDNA-HRP is cleaved by the activated CRISPR/Cas12a, resulting in the release of HRP and generating short DNA strands with 3-terminal hydroxyl on magnetic beads. The released HRP subsequently catalyzed TMB-H2O2 reaction and oxidized TMB is used for colorimetric and photothermal signal detection. Under the catalysis of terminal deoxynucleotidyl transferase (TdT), the remaining short DNA strands are used as primers to form poly-T and function as scaffolds to form copper nanoclusters for fluorescent signal output. To verify the practical application of CPF-CRISPR, we employed MRSA as a model. The results demonstrate the platform's high accuracy and sensitivity, with a limit of detection of 101 CFU/mL when combined with recombinase polymerase amplification. Therefore, by harnessing the programmability of CRISPR/Cas12a, the biosensor has the potential to detect various drug-resistant bacteria, demonstrating significant practical applicability.

Isoniazide modified Ag nanoparticles triggered photothermal immunoassay for carcinoembryonic antigen detection

As the most well-known analytical tool, the thermometer has been extended to the field of biological analysis based on the photothermal effect. Herein, isoniazide modified Ag nanoparticles were prepared as nanolabels to build an immunoassay. The nanoparticles were characterized by transmission electron microscope (TEM), dynamic laser scattering (DLS), X-ray powder diffraction (XRD), and Fourier transform infrared (FT-IR). When the target protein was present, the sandwich immunoassay was developed and the photothermal reaction was triggered by isoniazide modified Ag nanoparticles. As a reducing agent, isoniazide is used to transform phosphomolybdic acid hydrate into molybdenum blue solution. And molybdenum blue had good photothermal stability and high photothermal conversion efficiency. The temperature variation of molybdenum blue solution showed a positive correlation with the concentration of carcinoembryonic antigen (CEA). Thus, the target protein of CEA was quantitative detection by thermometer. The linear response range is 0.1 ng mL-1 to 40 ng mL-1, and the detection limit is 0.08 ng mL-1. Moreover, the proposed protocol had satisfactory selectivity, accuracy, and reproducibility.

Light-Driven Photocatalytic-Photothermal Synergetic System for Portable and Sensitive Nucleic Acid Quantification

Photosensitizers and photothermal agents have attracted increasing attention for in vitro diagnosis, but the combination remains challenging. Herein, a light-driven photocatalytic-photothermal synergetic system integrated microfluidic distance-based analytical device (PCPT-μDAD) for visual, portable, sensitive, and quantitative detection of targets was developed. Target DNA was recognized and initiated the hybridization chain reaction to form a double-stranded DNA/SYBR Green I (dsDNA/SG-I) complex. By applying the photosensitization of the dsDNA/SG-I complex and the photothermal effect of oxidized 3,3',5,5'-tetramethylbenzidine, the target concentration can effectively translate into a visual distance signal readout. Importantly, the light-driven PCPT-μDAD greatly improves the controllability of catalytic reactions and signal amplification efficiency. The light-driven PCPT-μDAD shows a low limit of detection (fM level), good stability, and high reproducibility for nucleic acid detection.

Optimization and Enhancement of the Peroxidase-like Activity of Hemin in Aqueous Solutions of Sodium Dodecylsulfate

Iron porphyrins play several important roles in present-day living systems and probably already existed in very early life forms. Hemin (= ferric protoporphyrin IX = ferric heme b), for example, is the prosthetic group at the active site of heme peroxidases, catalyzing the oxidation of a number of different types of reducing substrates after hemin is first oxidized by hydrogen peroxide as the oxidizing substrate of the enzyme. The active site of heme peroxidases consists of a hydrophobic pocket in which hemin is embedded noncovalently and kept in place through coordination of the iron atom to a proximal histidine side chain of the protein. It is this partially hydrophobic local environment of the enzyme which determines the efficiency with which the sequential reactions of the oxidizing and reducing substrates proceed at the active site. Free hemin, which has been separated from the protein moiety of heme peroxidases, is known to aggregate in an aqueous solution and exhibits low catalytic activity. Based on previous reports on the use of surfactant micelles to solubilize free hemin in a nonaggregated state, the peroxidase-like activity of hemin in the presence of sodium dodecyl sulfate (SDS) at concentrations below and above the critical concentration for SDS micelle formation (critical micellization concentration (cmc)) was systematically investigated. In most experiments, 3,3',5,5'-tetramethylbenzidine (TMB) was applied as a reducing substrate at pH = 7.2. The presence of SDS clearly had a positive effect on the reaction in terms of initial reaction rate and reaction yield, even at concentrations below the cmc. The highest activity correlated with the cmc value, as demonstrated for reactions at three different HEPES concentrations. The 4-(2-hydroxyethyl)-1-piperazineethanesulfonate salt (HEPES) served as a pH buffer substance and also had an accelerating effect on the reaction. At the cmc, the addition of l-histidine (l-His) resulted in a further concentration-dependent increase in the peroxidase-like activity of hemin until a maximal effect was reached at an optimal l-His concentration, probably corresponding to an ideal mono-l-His ligation to hemin. Some of the results obtained can be understood on the basis of molecular dynamics simulations, which indicated the existence of intermolecular interactions between hemin and HEPES and between hemin and SDS. Preliminary experiments with SDS/dodecanol vesicles at pH = 7.2 showed that in the presence of the vesicles, hemin exhibited similar peroxidase-like activity as in the case of SDS micelles. This supports the hypothesis that micelle- or vesicle-associated ferric or ferrous iron porphyrins may have played a role as primitive catalysts in membranous prebiotic compartment systems before cellular life emerged.

Construction of a Dual-Mode Immune Platform Based on the Photothermal Effect of AgCo@NC NPs for the Detection of α-Fetoprotein

Compared with the accuracy of a single signal and the limitation of environmental applicability, the application value of dual-mode detection is gradually increasing. To this end, based on the photothermal effect of Ag/Co embedded N-rich mesoporous carbon nanomaterials (AgCo@NC NPs), we designed a dual-mode signal response system for the detection of α-fetoprotein (AFP). First, AgCo@NC NPs act as a photothermal immunoprobe that converts light energy into heat driven by a near-infrared (NIR) laser and obtains temperature changes corresponding to the analyte concentration on a hand-held thermal imager. In addition, this temperature recognition system can significantly improve the efficiency of Fenton-like reactions. AgCo@NC NPs act as peroxidase mimics to initiate the generation of poly N-isopropylacrylamide (PNIPAM, resistance enhancer) by cascade catalysis and the degradation of methylene blue (MB), thus enabling electrochemical testing. The dual-mode assay ranges from 0.01 to 100 and 0.001-10 ng/mL, with lower limits of detection (LOD) of 3.2 and 0.089 pg/mL, respectively, and combines visualization, portability, and high efficiency, opening new avenues for future clinical diagnostics and inhibitor studies.

Nitrocellulose membranes in situ grown with Prussian blue nanoparticles as stable nanozyme pads for colorimetric detection of dopamine

Prussian blue (PB) is a typical peroxidase mimic with simple preparation, low cost and high eco-friendliness, but it still has drawbacks of poor stability (e.g., decomposition in aqueous dispersions) and intrinsic optical interference (e.g., high extinction coefficient over a wide wavelength range) in colorimetric assays. Herein, we used nitrocellulose (NC) membranes as synthesis hosts of PB nanoparticles (NPs) to develop a new type of three-dimensional (3D) porous nanozyme pad. By means of an in situ synthesis route, PB NPs were uniformly grown on the surfaces of the fiber scaffolds with desirable stability, which also avoided signal interference from PB NPs owing to the easy handling of the pads in a quantitative solid state. The pads showed significant peroxidase-mimicking activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with the output of colorimetric signals. Based on the reduction of oxidized TMB (oxTMB) by dopamine (DA), the pads were exploited for simple and quantitative colorimetric detection of DA with a limit of detection (LOD) of 0.59 μM and a satisfactory accuracy for analysis of real human urine samples. This is the first attempt at exploiting NC membranes as the synthesis hosts to develop nanozyme pads, which solves the above drawbacks of traditional PB-based peroxidase mimics and has promise for various colorimetric bioanalyses, given the structural benefits of NC membranes and their broad applications in biosensors.

Complementary Homogeneous Electrochemical and Photothermal Dual-Modal Sensor for Highly Sensitive Detection of Organophosphorus Pesticides via Stimuli-Responsive COF/Methylene Blue@MnO2 Composite

Credible and on-site detection of organophosphorus pesticides (OPs) in complex matrixes is significant for food security and environmental monitoring. Herein, a novel COF/methylene blue@MnO2 (COF/MB@MnO2) composite featured abundant signal loading, a specific recognition unit, and robust oxidase-like activity was successfully prepared through facile assembly processes. The multifunctional composite acted as a homogeneous electrochemical and photothermal dual-mode sensing platform for OPs detection through stimuli-responsive regulation. Without the presence of OPs, the surface MnO2 coating could recognize thiocholine (TCh), originating from acetylcholinesterase (AChE)-catalyzed hydrolysis of acetylthiocholine (ATCh), and exhibited a distinctly amplified diffusion current due to the release of plentiful MB; while the residual MnO2 nanosheets could only catalyze less TMB into oxidized TMB (oxTMB) with a typical near-infrared (NIR) absorption, enabling NIR-driven photothermal assay with a low temperature using a portable thermometer. Based on the inhibitory effect of OPs on AChE activity and OP-regulated generation of TCh, chlorpyrifos as a model target can be accurately detected with a low limit of detection of 0.0632 and 0.108 ng/mL by complementary electrochemical and photothermal measurements, respectively. The present dual-mode sensor was demonstrated to be excellent for application to the reliable detection of OPs in complex environmental and food samples. This work can not only provide a complementary dual-mode method for convenient and on-site detection of OPs in different scenarios but also expand the application scope of the COF-based multifunctional composite in multimodal sensors.

Cascaded Nanozyme with In Situ Enhanced Photothermal Capacity for Tumor-Specific and Self-Replenishing Cancer Therapy

Reactive oxygen species (ROS)-involved tumor therapeutic strategy, chemodynamic therapy (CDT), has attracted extensive research interest in the scientific community. However, the therapeutic effect of CDT is insufficient and unsustainable owing to the limited endogenous H2 O2 level in the tumor microenvironment. Here, peroxidase (POD)-like RuTe2 nanozyme with the immobilization of glucose oxidase (GOx) and allochroic 3,3',5,5'-tetramethylbenzidine (TMB) molecule have been synthesized to construct RuTe2 -GOx-TMB nanoreactors (RGT NRs) as cascade reaction systems for tumor-specific and self-replenishing cancer therapy. GOx in sequential nanocatalysts can effectively deplete glucose in tumor cells. Meanwhile, a sustainable supply of H2 O2 for subsequent Fenton-like reactions catalyzed by RuTe2 nanozyme is achieved in response to the mild acidic tumor microenvironment. Through this cascade reaction, highly toxic hydroxyl radicals (·OH) are produced, which can further oxidize TMB to trigger tumor-specific "turn-on" photothermal therapy (PTT). In addition, PTT and massive ROS can stimulate the tumor immune microenvironment and activate the systematic anti-tumor immune responses, exerting a notable effect on hindering tumor recurrence and metastasis. This study paves a promising paradigm for synergistic starvation therapy, PTT, and CDT cancer therapy with high efficiency.

Diazo-reaction based dual-mode colorimetric-electrochemical sensing of nitrite in pickled food

Development of an effective and convenient sensor for sensitive detection of nitrites is of great concern since excessive amounts of nitrites can be harmful to both human health and the environment. In this work, Cu-MOF modified exfoliated graphite paper (EGP) was employed as a signal reporter to enable the visual and electrochemical dual-mode sensing of nitrites. Cu-MOFs were in situ synthesized on EGP, which exhibited an excellent oxidase enzyme-like activity to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) into its oxidation product (oxTMB). The multi-layer structure and the superior electrical conductivity of EGP not only facilitated the loading of the Cu-MOF nanozyme for colorimetric sensing but also enabled its use as an underlying backbone to support electroanalysis. Based on the recognition of nitrite through a highly specific diazo reaction between nitrite and oxTMB, the addition of nitrite caused the colorimetric sensing solution to change color from blue to green, which allowed for the colorimetric sensing of nitrite with a limit of detection (LOD) of 8.5 × 10-6 mol L-1. Meanwhile, the Cu-MOF/EGP electrochemical platform was employed for ratiometric detection of nitrite based on the electrochemical oxidation of nitrite and TMB. Compared with the colorimetric mode, the electrochemical mode possessed higher sensitivity with a LOD of 5.4 × 10-7 mol L-1, indicating the high sensitivity and accuracy of the proposed dual-mode sensing strategy. Furthermore, the determination of nitrite in different pickled food samples is demonstrated.

Exploiting the Potential of Magnetic Nanoparticles for Rapid Diagnosis Tests (RDTs): Nanoparticle-Antibody Conjugates and Color Development Strategies

Magnetic nanoparticles (MNPs) have emerged as a promising material in disease diagnostics due to their potential to enhance detection sensitivity, facilitate concentration and purification of target substances in diverse samples, and enable favorable color-based detection. In this study, antibody-conjugated MNPs were successfully synthesized and validated through two appropriate methods: the measurement of MNPs' size and the use of phosphatase methods. Additionally, three methods were suggested and implemented for developing color in MNPs-based immunoassay, including the formation of MNP aggregations, utilization of MNPs' peroxidase-like activity, and synthesis of dually-conjugated MNPs with both enzyme and antibody. In particular, color development utilizing nanoparticle aggregations was demonstrated to result in a more yellowish color as virus concentration increased, while the peroxidase activity of MNPs exhibited a proportional increase in color intensity as the MNP concentration increased. This observation suggests the potential applicability of quantitative analysis using these methods. Furthermore, effective concentration and purification of target substances were demonstrated through the collection of MNPs using an external magnetic field, irrespective of factors such as antibody conjugation, dispersion medium, or virus binding. Finally, based on the key findings of this study, a design proposal for MNPs-based immunoassay is presented. Overall, MNPs-based immunoassays hold significant potential for advancing disease diagnostics.

Fluoride-activated photothermal system for promoting bacteria-infected wound healing

Although photothermal therapy (PTT) employing nanozymes has shown excellent antibacterial potential, excessive heating generally harms host cells and hinders recovery. Herein, we report an innovative technique for acquiring the programmed temperature by managing the catalytic activity of nanozymes. The photothermal system of CeO2 + F- + TMB can obtain precise photothermal temperature by adjusting the concentration of fluoride ions under near-infrared irradiation. At the optimized photothermal temperature, the photothermal system affords fine photothermal antibacterial treatment with high-efficiency antibacterial effects against Staphylococcus aureus and Escherichia coli in vitro. In vivo wound healing experiments confirm that the system can effectively promote fibroblast proliferation, angiogenesis and collagen deposition with remarkable wound healing efficiency. This strategy offers a novel design concept for creating a new generation of PTT and opens the way for the creation of alternative antibiotics.

Research Progress of SERS Sensors Based on Hydrogen Peroxide and Related Substances

Hydrogen peroxide (H2O2) has an important role in living organisms, and its detection is of great importance in medical, chemical, and food safety applications. This review provides a comparison of different types of Surface-enhanced Raman scattering (SERS) sensors for H2O2 and related substances with respect to their detection limits, which are of interest due to high sensitivity compared to conventional sensors. According to the latest research report, this review focuses on the sensing mechanism of different sensors and summarizes the linear range, detection limits, and cellular applications of new SERS sensors, and discusses the limitations in vivo and future prospects of SERS technology for the detection of H2O2.

Efficient Nanozyme-Triggered Pressure Sensor for Point-of-Care Immunoassay: Visual Sensing and Time Readout Device

Point-of-care testing (POCT), with its portability and high sensitivity, is an analytical device for rapid on-site sensing and detection. In this study, a POCT device was designed for the portable detection of illegal additives by integrating a coil device that can visually sense color distance and a two-electrode electrochemical system. Real-time monitoring of pressure changes was achieved by driving CeO₂@Pt/Au nanoparticle (NP)-labeled antibodies into a competitive immunoreaction, in which CeO₂ and Pt/Au synergistically catalyzed the production of large amounts of O₂ from H₂O₂, leading to a significant increase in gas within the closed chamber. Attractively, the coil device converted the pressure stimulus into visually readable change in distance for semi-quantitative detection of the target substance, while the electrical signal output caused by the changes of the solution around the electrodes achieved accurate and reliable quantification of the target. In addition, the proposed dual-mode pressure immunoassay device has acceptable selectivity, stability, and reproducibility. Herein, this portable device, which enables target concentration readings by converting pressure into multiple signals, provides an effective way to visualize POCT assays in resource-limited areas.

A label-free dually-amplified aptamer sensor for the specific detection of amyloid-beta peptide oligomers in cerebrospinal fluids

Amyloid-beta peptide oligomer (Aβo) is widely acknowledged to be associated with Alzheimer's disease (AD). The immediate and accurate detection of Aβo may provide the index for tracking the progress of the state of the disease, as well as some useful information for investigating the pathology of AD. In this work, based on a triple helix DNA which triggers a series of circular amplified reactions in the presence of Aβo, we designed a simple and label-free colorimetric biosensor with dually-amplified signal for the specific detection of Aβo. The sensor displays some advantages including high specificity, high sensitivity, low detection limit down to 0.23 pM, and wide detection range with three orders of magnitude from 0.3472 to 694.44 pM. Furthermore, the proposed sensor was successfully applied for detecting Aβo in artificial and real cerebrospinal fluids with satisfactory results, suggesting the potential application of the proposed sensor for state-monitoring and pathological studies of AD.

DNA-Driven Photothermal Amplification Transducer for Highly Sensitive Visual Determination of Extracellular Vesicles

Extracellular vesicles (EVs) are crucial focus of current biomedical research and future medical diagnosis. However, the requirement for specialized sophisticated instruments for quantitative readouts has limited the sensitive measurement of EVs to specialized laboratory settings, which in turn has limited bench-to-bedside translation of EV-based liquid biopsies. In this work, a straightforward temperature-output platform based on a DNA-driven photothermal amplification transducer was developed for the highly sensitive visual detection of EVs using a simple household thermometer. The EVs were specifically recognized by the antibody-aptamer sandwich immune-configuration that was constructed on portable microplates. Via a one-pot reaction, cutting-mediated exponential rolling circle amplification was initiated in situ on the EV surface, generating substantial G-quadruplex-DNA-hemin conjugates. Significant amplification in temperature was achieved from the effective photothermal conversion and regulation guided by the G-quadruplex-DNA-hemin conjugates in the 3,3',5,5'-tetramethylbenzidine-H2O2 system. Through obvious temperature outputs, the DNA-driven photothermal transducer enabled highly sensitive EV detection at close to the single-particle level and supported the highly specific identification of tumor-derived EVs directly in serum samples, without the requirement of any sophisticated instrument or labeling process. Benefiting from highly sensitive visual quantification, an easy-to-use readout, and portable detection, this photothermometric strategy is expected to be deliverable across professional on-site screening to home self-testing as EV-based liquid biopsies.

Ag/MoO3–Pd-mediated gasochromic reaction: An efficient dual-mode photoelectrochemical and photothermal immunoassay

Herein, we presented a dual-readout gasochromic immunosensing platform for accurate and sensitive detection of carcinoembryonic antigen (CEA) based on Ag-doped/Pd nanoparticles loaded MoO₃ nanorods (Ag/MoO₃-Pd). Initially, the presence of analyte CEA would prompt the formation of sandwich-type immunoreaction, accompanied by the introduction of Pt NPs labeled on detection antibody. Upon the addition of NH₃BH₃, the product hydrogen (H₂) will interact with Ag/MoO₃-Pd as a bridge between the sensing interface and the biological assembly platform. Both photocurrent and temperature signals can serve as readouts due to the significantly increased PEC performance and enhanced photothermal conversion capability of H-Ag/MoO₃-Pd (the product of Ag/MoO₃-Pd react with H₂) compared to Ag/MoO₃-Pd. In addition, the DFT results show that the band gap of Ag/MoO₃-Pd becomes narrower after the reaction with H₂, thus improving the utilization of light, which theoretically explains the internal mechanism of gas sensing reaction. Under optimal conditions, the designed immunosensing platform showed good sensitivity for CEA detection with the limit of detection (LOD) of 26 pg mL^-1 (photoelectrochemical mode) and 98 pg mL^-1 (photothermal mode). This work not only presents the possible reaction mechanism of Ag/MoO₃-Pd and H₂, but also creatively applicate it in photothermal biosensors that give a new path for devising dual-readout immunosensor.

Facile and portable multimodal sensing platform driven by photothermal-controlled release system for biomarker detection

Portable, maneuverable and reliable versatile-integrated analytical devices are urgently demanded but still extremely challenging to meet the requirements of point-of-care testing in resource-limited areas. Herein, a multifunctional sensing platform with excellent photothermal performance was implanted into the miniature zone of a paper-based electrochemiluminescent (ECL) biosensor for accurate detection of interleukin-6, which could flexibly interconnect the visualized distance and temperature readout with ultrasensitive ECL response. Concretely, the multipurpose MBene and TaSe₂ composites (MBene@TaSe₂) prepared via self-assembly approach as target-associated photothermal element was introduced in the paper-based analytical device (PAD) and served as multi-signals trigger. Under the laser irradiation, MBene@TaSe₂ probe not only generated heat for rapid temperature output, but also triggered the phase transition behavior of thermoresponsive poly (N-isopropylacrylamide) (pNIPAM) hydrogel to release loaded malachite green (MG) dye for distance-based visual readout. Simultaneously, the released MG was also utilized as effective quencher to decrease the ECL signal of luminol. Benefitting from this dexterous architecture, the speedy preliminary screening and precise quantitative analysis could be subsequently obtained in single-drop sample through one-step sandwich immunoreaction, which avoids additional separation operations and greatly simplifies the analysis procedure. Undeniably, this work provides ingenious insights for advancing the development of convenient and fast multifunction-integrated PAD in family surveillance and intelligent diagnosis.

Metal-mediated Fe3O4@polydopamine-aptamer capture nanoprobe coupling multifunctional MXene@Au@Pt nanozyme for direct and portable photothermal analysis of circulating breast cancer cells

Breast cancer (BC) is the most common cancer in the world and circulating tumor cells (CTCs) are reliable biomarkers for early breast cancer diagnosis in a non-invasive manner. However, effective isolation and sensitive detection of BC-CTCs by portable devices in human blood samples are extremely challenging. Herein, we proposed a highly sensitive and portable photothermal cytosensor for direct capture and quantification of BC-CTCs. To achieve efficient isolation of BC-CTCs, aptamer functionalized Fe₃O₄@PDA nanoprobe was facilely prepared through Ca²⁺-mediated DNA adsorption. To further detect the captured BC-CTCs with high sensitivity, multifunctional two-dimensional Ti₃C₂@Au@Pt nanozyme was synthesized, which not only possessed superior photothermal effect but also exhibited high peroxidase-like activity for catalyzing 3,3',5,5'-tetramethylbenzidine (TMB) to produce TMB oxide (oxTMB) with a strong photothermal characteristic, combining with Ti₃C₂@Au@Pt to synergistically amplify the temperature signal. Moreover, numerous Ti₃C₂@Au@Pt nanocomposites would be selectively attained on the BC-CTCs surface through multi-aptamer recognition and binding strategy, which further enhanced the specificity and facilitated signal amplification. Therefore, direct separation and highly sensitive detection of BC-CTCs was successfully achieved in human blood samples. More significantly, the controlled release of the captured BC-CTCs without affecting cell viability could be straightforwardly realized by a simple strand displacement reaction. Thus, with the distinct features of portability, high sensitivity, and easy operation, the current method holds great promise for early diagnosis of breast cancer.

Nanozyme-based dual-signal sensing system for colorimetric and photothermal detection of AChE activity in the blood of liver-injured mice

Acetylcholinesterase (AChE), a crucial enzyme related to liver function, is involved in numerous physiological processes such as neurotransmission and muscular contraction. The currently reported techniques for detecting AChE mainly rely on a single signal output, limiting their high-accuracy quantification. The few reported dual-signal assays are challenging to implement in dual-signal point-of-care testing (POCT) because of the need for large instruments, costly modifications, and trained operators. Herein, we report a colorimetric and photothermal dual-signal POCT sensing platform based on CeO₂-TMB (3,3',5,5'-tetramethylbenzidine) for the visualization of AChE activity in liver-injured mice. The method compensates for the false positives of a single signal and realizes the rapid, low-cost portable detection of AChE. More importantly, the CeO₂-TMB sensing platform enables the diagnosis of liver injury and provides an effective tool for studying liver disease in basic medicine and clinical applications. Rapid colorimetric and photothermal biosensor for sensitive detection of acetylcholinesterase (I) and acetylcholinesterase levels in mouse serum (II).

RPA-CRISPR/Cas12a Combined with Rolling Circle Amplification-Enriched DNAzyme: A Homogeneous Photothermal Sensing Strategy for Plant Pathogens

Alternaria is an endemic fungus associated with brown spot disease, which is one of the most serious citrus diseases. In addition, the mycotoxins metabolized by Alternaria threaten human health seriously. Herein, a novel homogeneous and portable qualitative photothermal method based on recombinase polymerase amplification (RPA), CRISPR/Cas12a, and rolling circle amplification (RCA) for the detection of Alternaria is described. Using RCA primers as substrates for CRISPR/Cas12a trans-cleavage, the two systems, RPA-CRISPR/Cas12a and RCA-enriched G-quadruplex/hemin DNAzyme, are intelligently combined. Target DNA at fg/μL levels can be detected with high specificity. Additionally, the practicability of the proposed method is demonstrated by analyzing cultured Alternaria from different fruit and vegetable samples, as well as citrus fruit samples collected in the field. Furthermore, the implementation of this method does not require any sophisticated equipment and complicated washing steps. Therefore, it has great potential to screen Alternaria in poor laboratories.

Advanced biosensors for mycotoxin detection incorporating miniaturized meters

Advanced biosensors, considered as emerging technologies, are capable of accurate, quantitative and real-time analysis for point-of-care testing (POCT) applications. Moreover, the integrating of miniaturized meters into these advanced biosensors makes them ideally appropriate for portable, sensitive and selective detection of biomolecules. Miniaturized meters including PGMs (personal glucose meters), thermometer, pressuremeter, pH meter, etc. are the most accurate devices and wide availability in the market, exhibiting a promising potential towards detection of small molecule mycotoxins. In this article, we introduce and analyze the recent advancements for sensing of mycotoxins measured by handheld meters since the first report in 2012. Furthermore, limitations and challenges for versatile meters application against mycotoxins in food matrix are highlighted. By overcoming the bottleneck problems, we believe the miniaturized meters-based biosensor platform will provide great possibilities for mycotoxins analysis and launch them to the market.

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

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

One-step synthesis of triethanolamine-capped Pt nanoparticle for colorimetric and electrochemiluminescent immunoassay of SARS-CoV spike proteins

Platinum nanoparticles (PtNPs) have been attracted worldwide attention due to their versatile application potentials, especially in the catalyst and sensing fields. Herein, a facile synthetic method of triethanolamine (TEOA)-capped PtNPs (TEOA@PtNP) for electrochemiluminescent (ECL) and colorimetric immunoassay of SARS-CoV spike proteins (SARS-CoV S-protein, a target detection model) is developed. Monodisperse PtNPs with an average diameter of 2.2 nm are prepared by a one-step hydrothermal synthesis method using TEOA as a green reductant and stabilizer. TEOA@PtNPs can be used as a nanocarrier to combine with antigen by the high-affinity antibody, which leads to a remarkable inhibition of electron transfer efficiency and mass transfer processes. On the basis of its peroxidase-like activity and easy-biolabeling property, the TEOA@PtNP can be used to establish a colorimetric immunosensor of SARS-CoV S-protein thought catalyzing the reaction of H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB). Especially, the Ru(bpy)3 2+ ECL reaction is well-achieved with the TEOA@PtNPs due to their great conductivity and loading abundant TEOA co-reactants, resulting in an enhancing ECL signal in immunoassay of SARS-CoV S-protein. As a consequence, two proposed methods could achieve sensitive detection of SARS-CoV S-protein in wide ranges, the colorimetric and ECL detection limits were as low as 8.9 fg /mL and 4.2 fg /mL (S/N = 3), respectively. We believe that the proposed colorimetric and ECL immunosesors with high sensitivity, good reproducibility, and good stability will be a promising candidate for a broad spectrum of applications.

Near Infrared-II Photothermal and Colorimetric Synergistic Sensing for Intelligent Onsite Dietary Myrosinase Profiling

Myrosinase (Myr) is a type of critical β-thioglucosidase enzyme activator essential for sustaining many functional foods to perform their health-promoting functions. An accurate and reliable Myr test is meaningful for food quality and dietary nutrition assessments, whereas the currently reported methods do not guarantee specificity and have high reliance on instrumentation, which are not suitable for rapid and onsite Myr screening especially in complex systems from various sources. Herein, we present a unique NIR-II absorption-based photothermal-responsive colorimetric biosensor for anti-interference onsite Myr determination and realization of rapid visualized outputs with the aid of smartphone calculation. Typically, assisted by glucose oxidase (GOx), Myr specifically converts the sinigrin substrate into hydrogen peroxide (H₂O₂) that can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) catalyzed by AuNPs to form a charge transfer complex (CTC) with NIR-II absorption and photothermal characters. Delightfully, such a proposed method is able to determine Myr within a wide range of 0 to 172.5 mU/mL with a detection limit down to 2.96 mU/mL. Moreover, simple, rapid, and real-time visual Myr identification in actual food-sourced samples could also be readily achieved by smartphone readout processing, with the promising advantages of anti-interference, high accuracy, and low cost as well as labor-saving and intelligence engagement, thus providing great feasibility for precise measurement in complex and dynamic dietary sample analysis. Overall, our proposed method presents a novel technology for onsite dietary Myr enzyme profiling, which is promising to be applied in the food industry for nutritional composition profiles, freshness evaluation, and quality assessment.

SERS-based error calibration of a TMB-H2O2 colorimetric system

3,3',5,5'-tetramethylbenzidine (TMB)-H₂O₂ is widely used as an effective colorimetric system, in which the color reaction is implemented with peroxidase-catalyzed TMB oxidation by H₂O₂ that usually measured UV-vis absorption spectra or Raman spectra. However, its low accuracy significantly limits its application. Blue charge transfer complex (CTC), which is the product of TMB and H₂O₂ reaction and is used as the basis for partial colorimetric methods, usually causes colorimetric error owing to changes in the UV-vis absorption and Raman spectra during TMB oxidation under various environmental conditions (catalyst type, temperature, H₂O₂ concentration). Herein, we propose a surface-enhanced Raman spectrum (SERS)-based error calibration method to improve the accuracy of the TMB-H₂O₂ colorimetric system. It is found that under 633 nm laser excitation, TMB has three Raman peaks at 1189, 1335 and 1609 cm^-1 in the single-electron oxidation phase, and these peaks disappear completely in the two-electron oxidation phase. By comparing these Raman peaks, we can conveniently obtain the actual process information during TMB oxidation. Using the proposed method, the accuracy of the TMB-H₂O₂ colorimetric system improved by more than 15%. Importantly, this SERS-based TMB-H₂O₂ error calibration method will open a new horizon for enzyme-linked immunosorbent assay (ELISA) and other biomedical applications.

Aptamer-Engineered Cu2O Nanocubes as a Surface-Modulated Catalytic Optical Sensor for Lung Cancer Cell Detection

Herein, fine and homogeneous Cu₂O nanocubes are synthesized and sensitized with a hairpin-structured AS1411 aptamer for the establishment of a biosensor for lung cancer cell detection. The Apt-Cu₂O nanocubes feature a recognition function in identifying a cancer-associated surface nucleolin protein. The intrinsic reduction catalytic ability is also confirmed by the use of two benchmark substrates, methylene blue (MB) and 4-nitrophenol (4-NP). The aptamer grafting on Apt-Cu₂O nanocubes is able to greatly prevent nonspecific-protein binding and to show specificity toward the nucleolin protein. The specific binding resulting from nucleolin protein leads to less exposure of the active area of the Apt-Cu₂O nanocubes, so the catalytic ability of Apt-Cu₂O nanocubes is thus diminished. The modulated catalytic ability led to less generation of the reduced 4-AP product, and the change in absorption of 4-AP allows the quantification of the nucleolin protein with a detection limit of 0.47 nM. The as-developed biosensor is applied to the detection of nucleolin-overexpressed A549 lung cancer cells, presenting a sensitive detection limit down to 20 cells. This may be ascribed to the clustering of surface nucleolin protein in a lipid raft membrane of cancer cells, as evidenced by a notable binding of Apt-Cu₂O nanocubes on the cancer cell surface. Real human serum samples spiked with cancer cells were also investigated, and a recovery rate of 87 ± 2.4% for 20 extracted cells validates the surface-modulated Apt-Cu₂O nanocubes-based catalytic optical biosensor as a promising tool for the detection of circulating tumor cells. The establishment of the Apt-Cu₂O nanocubes may allow for further studies on their use as a potential theranostics tool for cancer therapy.

Cerium/polyacrylic acid modified porphyrin metal-organic framework as fluorescence and photothermal sensor for ascorbic acid measurement

A fluorescence and photothermal dual-signal assay was developed for the determination of ascorbic acid (AA). Cerium/polyacrylic acid modified porphyrin metal-organic frameworks (PCN-224@PAA-Ce MOFs) exhibit oxidase-like activity and can effectively oxidize 3,3 ', 5,5 '-tetramethylbenzidine (TMB) from colorless substrates to blue substrates (oxTMB). The absorption spectrum of oxTMB overlaps with the emission spectrum of PCN-224@PAA-Ce, resulting in quenching of fluorescence emission of PCN-224@PAA-Ce. oxTMB, as an excellent photothermal agent, converts the optical signal into the thermal signal (temperature increasing) driven by 808 nm laser. In the presence of AA, the blue oxTMB was reduced to colorless TMB, which led to the fluorescence recovery of PCN-224@PAA-Ce and at the same time, the photothermal signal was changed with the temperature decreasing under the driving of 808 nm laser. The detection limits (LOD) of fluorescence/photothermal dual-mode AA sensor strategies were as low as 0.73 μM and 1.4 μM, respectively. Rapid analysis of ascorbic acid was accomplished with the present procedure, AA in vitamin C tablets and human serum samples were validated.

Colorimetric/photothermal dual-mode sensing detection of ascorbic acid based on a Ag[i] ion/3,3',5,5'-tetramethylbenzidine (TMB) system

In this work, a novel strategy of colorimetric and photothermal dual-mode sensing determination of ascorbic acid (AA) based on a Ag⁺/3,3',5,5'-tetramethylbenzidine (TMB) system was developed. In this sensing system, Ag⁺ could oxidize TMB with a distinct color change from colorless to blue color, strong absorbance at 652 nm and a photothermal effect under 808 nm laser irradiation due to the formation of oxidized TMB (oxTMB). When AA was present, oxTMB was reduced accompanied by a change from blue to colorless, and a decrease in absorption peak intensity and the photothermal effect. AA concentration showed a negative linear correlation with the value of both the absorbance intensity at 652 nm and temperature in the range of 0.2-10 μM (A = -0.03C + 0.343 (R ², 0.9887; LOD, 50 nM); ΔT = -0.57C + 8.453 (R ², 0.997; LOD, 7.8 nM)). Based on this, a sensing approach for detection of AA was proposed with dual-mode and without the complicated synthesis of nanomaterials. The photothermal effect and colorimetric signal provided a dual-mode detection strategy for AA, overcoming the limitations of any single mode. This colorimetric and photothermal dual-mode detection has great potential in the detection of AA in clinical pharmaceuticals and the construction of portable and highly sensitive sensors.