Biomimicking synthesis of photoluminescent molecular lantern catalyzed by in-situ formation of nanogold catalysts

Emerging Strategies in Enhancing Singlet Oxygen Generation of Nano-Photosensitizers Toward Advanced Phototherapy

The great promise of photodynamic therapy (PDT) has thrusted the rapid progress of developing highly effective photosensitizers (PS) in killing cancerous cells and bacteria. To mitigate the intrinsic limitations of the classical molecular photosensitizers, researchers have been looking into designing new generation of nanomaterial-based photosensitizers (nano-photosensitizers) with better photostability and higher singlet oxygen generation (SOG) efficiency, and ways of enhancing the performance of existing photosensitizers. In this paper, we review the recent development of nano-photosensitizers and nanoplasmonic strategies to enhance the SOG efficiency for better PDT performance. Firstly, we explain the mechanism of reactive oxygen species generation by classical photosensitizers, followed by a brief discussion on the commercially available photosensitizers and their limitations in PDT. We then introduce three types of new generation nano-photosensitizers that can effectively produce singlet oxygen molecules under visible light illumination, i.e., aggregation-induced emission nanodots, metal nanoclusters (< 2 nm), and carbon dots. Different design approaches to synthesize these nano-photosensitizers were also discussed. To further enhance the SOG rate of nano-photosensitizers, plasmonic strategies on using different types of metal nanoparticles in both colloidal and planar metal-PS systems are reviewed. The key parameters that determine the metal-enhanced SOG (ME-SOG) efficiency and their underlined enhancement mechanism are discussed. Lastly, we highlight the future prospects of these nanoengineering strategies, and discuss how the future development in nanobiotechnology and theoretical simulation could accelerate the design of new photosensitizers and ME-SOG systems for highly effective image-guided photodynamic therapy.

Bio-Templating: An Emerging Synthetic Technique for Catalysts. A Review

In the last few years, researchers have focused their attention on the synthesis of new catalyst structures based on or inspired by nature. Biotemplating involves the transfer of biological structures to inorganic materials through artificial mineralization processes. This approach offers the main advantage of allowing morphological control of the product, as a template with the desired morphology can be pre-determined, as long as it is found in nature. This way, natural evolution through millions of years can provide us with new synthetic pathways to develop some novel functional materials with advantageous properties, such as sophistication, miniaturization, hybridization, hierarchical organization, resistance, and adaptability to the required need. The field of application of these materials is very wide, covering nanomedicine, energy capture and storage, sensors, biocompatible materials, adsorbents, and catalysis. In the latter case, bio-inspired materials can be applied as catalysts requiring different types of active sites (i.e., redox, acidic, basic sites, or a combination of them) to a wide range of processes, including conventional thermal catalysis, photocatalysis, or electrocatalysis, among others. This review aims to cover current experimental studies in the field of biotemplating materials synthesis and their characterization, focusing on their application in heterogeneous catalysis.

Insights and Perspectives Regarding Nanostructured Fluorescent Materials toward Tackling COVID-19 and Future Pandemics

The COVID-19 outbreak has exposed the world's preparation to fight against unknown/unexplored infectious and life-threatening pathogens. The unavailability of vaccines, slow or sometimes unreliable real-time virus/bacteria detection techniques, insufficient personal protective equipment (PPE), and a shortage of ventilators and many other transportation equipments have further raised serious concerns. Material research has been playing a pivotal role in developing antimicrobial agents for water treatment and photodynamic therapy, fast and ultrasensitive biosensors for virus/biomarkers detection, as well as for relevant biomedical and environmental applications. It has been noticed that these research efforts nowadays primarily focus on the nanomaterials-based platforms owing to their simplicity, reliability, and feasibility. In particular, nanostructured fluorescent materials have shown key potential due to their fascinating optical and unique properties at the nanoscale to combat against a COVID-19 kind of pandemic. Keeping these points in mind, this review attempts to give a perspective on the four key fluorescent materials of different families, including carbon dots, metal nanoclusters, aggregation-induced-emission luminogens, and MXenes, which possess great potential for the development of ultrasensitive biosensors and infective antimicrobial agents to fight against various infections/diseases. Particular emphasis has been given to the biomedical and environmental applications that are linked directly or indirectly to the efforts in combating COVID-19 pandemics. This review also aims to raise the awareness of researchers and scientists across the world to utilize such powerful materials in tackling similar pandemics in future.

Recent development of nucleic acid nanosensors to detect sequence-specific binding interactions: From metal ions, small molecules to proteins and pathogens

DNA carries important genetic instructions and plays vital roles in regulating biological activities in living cells. Proteins such as transcription factors binds to DNA to regulate the biological functions of DNA, and similarly many drug molecules also bind to DNA to modulate its functions. Due to the importance of protein-DNA and drug-DNA binding, there has been intense effort in developing novel nanosensors in the same length scale as DNA, to effectively study these binding interactions in details. In addition, aptamers can be artificially selected to detect metal ions and pathogens such as bacteria and viruses, making nucleic acid nanosensors more versatile in detecting a large variety of analytes. In this minireview, we first explained the different types and binding modes of protein-DNA and drug-DNA interactions in the biological systems, as well as aptamer-target binding. This was followed by the review of five types of nucleic acid nanosensors based on optical or electrochemical detection. The five types of nucleic acid nanosensors utilizing colorimetric, dynamic light scattering (DLS), surface-enhanced Raman spectroscopy (SERS), fluorescence and electrochemical detections have been recently developed to tackle some of the challenges in high-throughput screening technology for large scale analysis, which is especially useful for drug development and mass screening for pandemic outbreak such as SARS or COVID-19.

Protein-protected gold/silver alloy nanoclusters in metal-enhanced singlet oxygen generation and their correlation with photoluminescence

Photoluminescent noble metal nanoclusters (NCs, core size <2 nm) have recently emerged as a new type of photosensitizers advantageous over conventional photosensitizers due to their high singlet oxygen (¹O₂) generation efficiency, excellent photostability and water solubility, as well as good biocompatibility for photodynamic therapy and bioimaging. However, no correlation has been established between the intrinsic ¹O₂ generation and photoluminescence properties of metal NCs with their size, composition, and concentration, which is important to customize the molecule-like properties of NCs for different applications. Herein, we report a systematic study to uncover the rational design of bimetallic NCs with controllable ¹O₂ generation efficiency by tuning their compositions through spontaneous galvanic displacement reaction. A series of ultrasmall gold/silver alloy nanoclusters (AuAgNCs) were synthesized by reacting bovine serum albumin (BSA) protein-protected Ag₁₃NCs (13 Ag atoms/cluster) with varying concentrations of gold precursor at room temperature. It was found that the ¹O₂ generation efficiency of the resultant BSA-protected AuAgNCs were inversely correlated to their photoluminescence intensity. Interestingly, plasmonic gold nanoparticles (>10 nm) were also formed simultaneously by photobleaching of the BSA-AuAgNCs, leading to significant metal enhancement effect to the ¹O₂ generation rate much higher (~45 times) than that of the monometallic BSA-Ag₁₃NC. This versatile two-for-one strategy to develop next generation metal-enhanced bimetallic NC photosensitizers in one pot opens up new opportunities in designing advanced hybrid nanomaterials with complementary and/or enhanced functionalities.

Nanodot-Directed Formation of Plasmonic-Fluorescent Nanohybrids toward Dual Optical Detection of Glucose and Cholesterol via Hydrogen Peroxide Sensing

Hybrid nanoparticles (NPs) have emerged as an important class of nanomaterials owing to their integrated enhanced properties and functionality. In this study, we have developed an effective nanodot templating strategy for the in situ formation of surfactant-free nanohybrids with unique plasmonic-fluorescent properties. A bright photoluminescent biodot synthesized from serine and histamine biomolecular precursors (Ser-Hist dot) was first engineered to have rich functional groups on the nanosurface capable of anchoring Ag⁺ ions via electrostatic interaction. Upon UV irradiation, free electrons could transfer from the photoexcited Ser-Hist dot to the Ag⁺ ions, facilitating the in situ growth of AgNPs. The resulting nanohybrid system (Bio@AgNPs) exhibits distinct characteristic surface plasmon resonance absorbance and highly quenched PL intensity due to the inner filter effect. Furthermore, the Bio@AgNP nanohybrid retains its redox capability, enabling hydrogen peroxide sensing via AgNP etching, which in turn empowers a dual colorimetric and fluorescent detection of glucose and cholesterol in complex biological samples (i.e., synthetic urine and human plasma) with high selectivity and sensitivity. This finding reveals a new effective and facile method for the preparation of highly functional hybrid nanomaterials for dual-mode detection of hydrogen peroxide-producing species and/or reactions.