Accurate SERS monitoring of the plasmon mediated UV/visible/NIR photocatalytic and photothermal catalytic process involving Ag@carbon dots

Ag-carbon dots with peroxidase-like activity for colorimetric and SERS dual mode detection of glucose and glutathione

Currently, nanozymes have made important research progress in the fields of catalysis, biosensing and tumor therapy, but most of nanozymes sensing systems are single-mode detection, which are easily affected by environment and operation, so it is crucial to construct nanozymes sensing system with dual-signal detection to obtain a more stable and reliable performance. In this paper, Ag-carbon dots (Ag-CDs) bifunctional nanomaterials were synthesized using carbon dots as reducing agent and protective agent by a facile and green one-step method. A simple and sensitive colorimetric-SERS dual-mode sensing platform was constructed for the detection of glucose and glutathione(GSH) in body fluids by taking advantage of good peroxidase-like and SERS activities of Ag-CDs. Ag-CDs catalyzes H2O2 to hydroxyl radicals(•OH), which oxidized TMB to form ox-TMB blue solution with characteristic absorption peak at 652 nm and Raman characteristic peak at 1607 cm-1. Ag-CDs sensing method exhibited high performance for glucose and GSH with detection limits for colorimetric and SERS as low as 11.30 μM and 3.54 μM, 0.38 μM and 0.24 μM respectively (S/N = 3). In addition, Ag-CDs have good stability and uniformity, ensuring long-term applicability of catalytic system. This colorimetric-SERS dual-mode sensing platform can be used for the determination of glucose and GSH in saliva and urine, and has the advantages of simple, low cost, rapid, and high accuracy, which has a potential application prospect in biosensor and medical research.

Difunctional AuNPs@PVP with oxidase-like activity for SERRS detection of total antioxidant capacity

Assessing the total antioxidant capacity (TAC) of foods plays a significant role in dietary guidance and disease risk reduction. Therefore, building a simple, rapid, and sensitive sensing method for detecting TAC possesses broad application prospects. Herein, we constructed a novel nanozyme catalyzed‒surface-enhanced Raman resonance scattering (SERRS) sensing strategy for analysis of TAC based on polyvinylpyrrolidone coated gold nanoparticles (AuNPs@PVP) that was synthesized by one step reduction method. AuNPs@PVP not only served as the SERRS substrate but also possessed high oxidase activity which can catalyze 3,3',5,5'-tetramethylbenzidine (TMB) oxidation by generating hydroxyl radicals (•OH) and superoxide anion free radical (•O2-). According to the inhibiting effect of antioxidants, ascorbic acid (AA) was selected as the representative for TAC detection. The linear range and limit of detection (LOD) were determined to be 10-8‒10-5 M and 0.6 nM, respectively. More importantly, the proposed nanozyme catalyzed‒SERRS strategy has been successfully applied to the detection of TAC in fruit juices, demonstrating promising potential in the field of food supervision and healthcare applications.

Nanozyme catalyzed-SERRS sensor for the recognition of dopamine based on AgNPs@PVP with oxidase-like activity

Dopamine (DA), as one of the most significant neurotransmitters, is closely related to several diseases. Achieving rapid and sensitive detection of DA remains a challenge. Herein, we proposed a simple, fast, and sensitive method for DA recognition based on surface-enhanced resonance Raman scattering (SERRS) technique. The synthesized silver nanoparticles coated with polyvinylpyrrolidone (AgNPs@PVP) with oxidase activity could not only oxidize 3,3',5,5'-tetramethylbenzidine (TMB) directly to produce a blue oxidation state TMB (oxTMB) but also could be used as the SERS substrate to generate a strong SERRS signal. When DA was added to the above system, the blue color faded along with the decrease in the SERRS signal. The change value of SERRS intensity was in proportion to the concentration of DA in the range of 0.1-10 μM with a limit of detection of 40 nM. This method presented great potential for the recognition of DA-related diseases.

Coupling Au-loaded magnetic frameworks to photonic crystal for the improvement of photothermal heating effect in SERS

The combination of plasmonic metals and photonic crystal (PC) structure is considered to have potential for further enhancement of the surface-enhanced Raman scattering (SERS) effect in comparison with conventional metal SERS substrates. Many studies have suggested that SERS signals probably suffer from an often-neglected effect of strong surface plasmon resonance (SPR)-induced photothermal heating during SERS detection. Herein, we have discovered that the photothermal heating problem arises in a traditional hybrid substrate that is prepared by doping plasmonic Au nanoparticles (NPs) into the voids of an opal PC (Au-PC). This happens mainly because excess Au agglomerates formed by non-uniformly distributed Au NPs can cause a strong SPR effect under laser illumination. To fully address this issue, we have employed an improved hybrid substrate that is fabricated by substituting Au NPs in Au-PC with an Au-loaded magnetic framework (AuMF). The AuMF can effectively prevent the aggregation of Au NPs and ensure sufficient hot spots for SERS. This novel substrate prepared by doping AuMFs into a PC (AuMF-PC) was free of strong photothermal heating and showed high SERS intensity and reproducibility of the SERS signal compared with Au-PC. For practical applications, we have demonstrated AuMF-PC as an appropriate candidate for the SERS assay of the trace thiol pesticide thiram, and it enables recycling and reuse to achieve low cost.

SERS monitoring of photoinduced-enhanced oxidative stress amplifier on Au@carbon dots for tumor catalytic therapy

Currently, artificial enzymes-based photodynamic therapy (PDT) is attractive due to its efficient capacity to change the immunosuppressive tumor microenvironment (TME). It is of great significance to study the therapeutic mechanism of novel artificial enzymes in TME through a monitoring strategy and improve the therapeutic effect. In this study, Au@carbon dots (Au@CDs) nanohybrids with a core-shell structure are synthesized, which not only exhibit tunable enzyme-mimicking activity under near-infrared (NIR) light, but also excellent surface-enhanced Raman scattering (SERS) properties. Therefore, Au@CDs show a good capability for monitoring NIR-photoinduced peroxidase-like catalytic processes via a SERS strategy in tumor. Moreover, the Au@CDs deplete glutathione with the cascade catalyzed reactions, thus elevating intratumor oxidative stress amplifying the reactive oxygen species damage based on the NIR-photoinduced enhanced peroxidase and glutathione oxidase-like activities, showing excellent and fast PDT therapeutic effect promoted by photothermal property in 3 min, finally leading to apoptosis in cancer cells. Through SERS monitoring, it is further found that after removing the NIR light source for 33 min, the reactive oxygen species (ROS) activity of the TME is counteracted and eliminated due to the presence of glutathione. This work presents a guidance to rationally design of artificial enzyme for ROS-involved therapeutic strategies and a new spectroscopic tool to evaluate the tumor catalytic therapy.

Combination of Plasmon-Mediated Photochemistry and Seed-Mediated Methods for Synthesis of Bicomponent Nanocrystals

Plasmon resonances of metal nanocrystals resulted from free electrons oscillating around nanocrystals, leading to a strong electromagnetic field around them. Because these oscillating electrons possess higher energy than the original ones, also known as hot electrons, these were widely used as photocatalysts for various reactions. Also, the strength and distribution of the electromagnetic field around the nanocrystals strongly depended on their morphology and excited irradiation, which led to the reaction environment around nanocrystals being controllable. Here, we integrated the seed-mediated and plasmon-mediated photochemistry methods for fabricating bimetallic and semiconductor-metal nanocrystals with controllable morphologies and compositions of the nanocrystals, resulting from the highly anisotropic reaction environment around the nanocrystals. The highly anisotropic reaction environment around the template nanocrystal was caused by the distribution of electromagnetic fields around it and its exposure area in the reaction solution. This new synthesis method should enable the fabrication of various multicomponent nanocrystals with desirable functions for potential applications, such as photocatalysts, chemical sensors, biosensors, biomedicines, etc.

Synergistic function of Au NPs/GeO2 nanozymes with enhanced peroxidase-like activity and SERS effect to detect choline iodide

A novel Au NPs/GeO₂ nanozymes are developed as Surface-Enhanced Raman Scattering (SERS) substrates with the promising prospect for detection ChI. Herein, it is discovered that both Au NPs and GeO₂ nanozymes have peroxidase-like activity, catalyzing colorless 3,3',5,5'-tetramethylbenzidine (TMB) to produce blue TMB_ox. Interestingly, compared with single Au NPs or GeO₂ nanozymes, the Au NPs/GeO₂ nanozymes show stronger peroxidase-like activity, and significantly ameliorated SERS signal of TMB_ox. The mentioned two enhancements are ascribed to a positive synergistic function of Au NPs/GeO₂ nanozymes. Surprisingly, choline iodide (ChI) can inhibit the positive synergy in Au NPs/GeO₂ nanozymes, and slow down the reaction of TMB-H₂O₂-Au NPs/GeO₂ system. On this foundation, a new Au NPs/GeO₂ SERS technique with high sensitivity, label-free detection method of choline iodide (ChI) is established, suggesting that Au NPs/GeO₂ nanozymes have the potential application of water environment.

Layered and orthogonal assembly of hydrophilic drugs and hydrophobic photosensitizers for enhanced cancer therapy

Combinatorial tumor therapy including chemotherapy and photodynamic therapy (PDT) can compensate for the limitations of each other and significantly increase the therapeutic effect. However, considering the differences of water-soluble characteristics between chemotherapeutic drugs and photosensitizers for photodynamic therapy, simply loading these substances into the same cavities of nanocarriers is rather difficult, leading to the reduced drug loading efficiency. Here, we reported a layered and orthogonal assembly of hydrophilic drugs doxorubicin (Dox) and hydrophobic photosensitizers Chlorin e6 (Ce6) for enhancing the effect of synergistic therapeutics. The assembly was based on polydopamine (PDA) modified with β-cyclodextrin (β-CD) through the addition reaction of -HS in HS-β-CD and-C=C in PDA, then DOX and Ce6 were loaded on the PDA and in the hydrophobic cavities of β-CDs respectively with superior drug loading efficiencies (38.8 ± 0.8% and 5.4 ± 0.3% for DOX and Ce6). PDA was hydrolyzed completely under the lysosomal acidic condition, leading to the controlled release of DOX. Under NIR irradiations, DOX-based chemotherapy was successfully integrated with PDA-based photothermal and Ce6-based photodynamic therapy. Tumor specific aptamer AS1411-modified assembly provides ideal antitumor effects in vitro and in vivo with excellent biocompatibility. Collectively, this layered and orthogonal assembly offers a generalizable solution for delivering matters with distinct aqueous solubility would find broad applications not only in drug delivery but also in bio-nanotechnology.

Recent Advances in Functional Carbon Quantum Dots for Antitumour

Carbon quantum dots (CQDs) are an emerging class of quasi-zero-dimensional photoluminescent nanomaterials with particle sizes less than 10 nm. Owing to their favourable water dispersion, strong chemical inertia, stable optical performance, and good biocompatibility, CQDs have become prominent in biomedical fields. CQDs can be fabricated by “top-down” and “bottom-up” methods, both of which involve oxidation, carbonization, pyrolysis and polymerization. The functions of CQDs include biological imaging, biosensing, drug delivery, gene carrying, antimicrobial performance, photothermal ablation and so on, which enable them to be utilized in antitumour applications. The purpose of this review is to summarize the research progress of CQDs in antitumour applications from preparation and characterization to application prospects. Furthermore, the challenges and opportunities of CQDs are discussed along with future perspectives for precise individual therapy of tumours.