Dual-Mode Gold Nanocluster-Based Nanoprobe Platform for Two-Photon Fluorescence Imaging and Fluorescence Lifetime Imaging of Intracellular Endogenous miRNA

Recent advances in fluorescent nanomaterials designed for biomarker detection and imaging

The highly sensitive detection and imaging of biomarkers are critical for early diagnosis, treatment, and prognosis monitoring. The unique size and structure of fluorescent nanomaterials provide key benefits such as excellent photostability, high fluorescence quantum yield, and tunable excitation and emission wavelengths. These properties have led to the widespread application of nanomaterials in fluorescent biomarkers detection and imaging. In this review, we began by introducing the composition of fluorescent probes and discussing the underlying sensing mechanisms. We then summarized recent advances in the use of fluorescent nanomaterials such as quantum dots (QDs), metal nanoclusters (MNCs), carbon dots (CDs), and metal-organic frameworks (MOFs) for biomarker detection and imaging. Additionally, we highlighted the applications of fluorescent nanomaterials in the detection and imaging of small molecules, biomacromolecules, and various biomarkers, including metal ions, bacteria, and circulating tumor cells (CTCs). The challenges and future prospects of fluorescent nanomaterials in biomarker detection and imaging were also discussed. We anticipate that fluorescent nanomaterials will have profound implications for clinical biomarker detection and imaging, with considerable application in both academic research and industrial applications.

Binary light-up fluorescent probe based on silver nanoclusters for MicroRNA detection

Silver nanoclusters (Ag NCs) are widely applied in the biosensing of metal ions, small organic molecules, nucleic acids, amino acids, and proteins due to their particular fluorescence and chemical properties. Organic matrices such as DNA are usually employed for Ag NC synthesis and stabilization. They make Ag NC/matrix complexes biocompatible and sensitive to the environment. It has recently been shown that Ag NCs based on DNA matrices are capable of self-assembly and rearrangement followed by a change in the fluorescence and absorbance characteristics. These attributes allow the development of sensors with target molecule detection visible even by the naked eye. Here we suggest a simple one-step turn-on highly specific microRNA-210 sensor based on a fluorescent Ag NC. The main feature of the sensor is the smart design of a binary matrix, which provides the appearance of a bright green fluorescence signal only after Ag NCs/DNA-matrix complexes are bonded to the target sequence. The microRNA detection assay requires no additional action because the process proceeds by itself. A comprehensive optimization of the binary probe structure and location was carried out. An approach to detection leading to minimal background signal was defined as follows. The approach involves the preliminary synthesis of non-fluorescent silver clusters using a single strand of the binary matrix containing a 5'-CCCGTTTT-3' part. It was shown that these "dark" structures can be stored for at least a month before analysis. The fluorescence intensity of the green Ag NCs increases in the presence of the microRNA-210 sequence, and that dependence on the target concentration tends to be linear in the range of 5-500 nM. The sensor demonstrates specificity to the miR-210 sequence, and the LOD (limit of detection) was established as 5 nM in serum samples.

Homogeneous Multicycle Cascaded DNA Circuit for Sensitive "Signal On-Off-Super On" PEC Biosensing

The minor changes of miRNA levels due to various diseases and cancers bring great challenges for early diagnosis. Here we propose a "signal on-off-super on" PEC biosensor based on a homogeneous multicycle cascaded DNA circuit and a SnSe/CdS photoanode for sensitive detection of biomarker miRNA-222. Specifically, a Z-type SnSe/CdS heterojunction with greatly enhanced photoanodic performance was developed to provide the initial "on" signal. The target miRNA-222 was converted to a dendritic DNA structure through a cascade DNA circuit. The PEC signal can be switched off by the dendritic DNA structure and further switched super on by the loading of photosensitizer manganese porphyrin (MnPP). It is worth noting that the homogeneous multicycle cascaded DNA circuit not only improved the reaction kinetics but also avoided the leakage of signal. Compared with the traditional "signal-on" or "signal-off" readout, this "signal on-off-super on" strategy avoids the false response and background, thereby enhancing the sensitivity and accuracy of the PEC biosensor. The detection limit of the constructed PEC sensor is 0.3 fM in the linear range from 1 fM to 10 nM. The PEC biosensor with outstanding reproducibility, stability, and sensitivity provides a promising platform for biomarker detection and early disease diagnosis.

Electrochemiluminescence and fluorescence dual-mode monitoring of aflatoxin B1 production based on single Ru-MOF particles and FITC luminophores

Herein, an electrochemiluminescence (ECL) and fluorescence (FL) dual-mode imaging biosensing platform was developed for onsite and dynamic monitoring of aflatoxin B1 (AFB1) production in the corn molding process. Zinc metal organic framework structures encapsulated with Ru(bpy)32+ (Ru-MOF) were employed as ECL signal probes for single particle imaging with stable luminescent intensity and high emission efficiency. Fluorescein Isothiocyanate (FITC) luminophores, served as fluorescent probes, were conjugated with AFB1 aptamer modified on the electrode surface, which enabled the observation of green luminescent spots in FL mode. When exposed to target AFB1, FITC luminophores detached from the surface of electrode, leading to a notable decrease in the number of green luminescent spots. Single Ru-MOF particles were then immobilized onto the surface of electrode through DNA coupling and discernible luminescent spots could be watched in ECL mode. Under optimal circumstances, a dual-mode imaging platform was constructed for AFB1 determination with a linear relationship of 1.0 fg/mL to 1.0 pg/mL in both ECL and FL mode. The detection limit (LOD) was 0.89 fg/mL in FL mode and 0.84 fg/mL in ECL mode, which demonstrated superior sensitivity. The imaging biosensor was established for dynamic tracking of AFB1 production in corn molding process. The results showed that aflatoxin production occurred more rapidly at damaged areas of the corn compared to areas with intact surfaces. The intact corn got moldy on the third day and its surface AFB1 concentration was calculated as 14.16 fg/mL. Combining the ECL and FL imaging technology with dual-mode biosensing, this work achieves high sensitivity, accuracy and capability of dynamic monitoring for AFB1 sensing which provides innovative ideas for the rational design of aflatoxin sensors, and holds substantial promise in food safety.

Fluorine-Nitrogen Codoped Carbon Dots for Visualization Imaging of Nucleic Acids via Two-Photon Fluorescence Lifetime Microscopy

Fluorescence imaging is a key tool for visualizing the morphology and dynamics of nucleic acids (DNA and RNA) in living cells to understand their role in regulating the growth, development, and reproduction of organisms. However, effective probes capable of simultaneously targeting both DNA and RNA, as well as tools for analyzing their distribution and relative ratios in organisms, are currently lacking. Therefore, fluorine-nitrogen codoped carbon dots with two-photon absorption (F-NCDs) were synthesized by the hydrothermal method and exhibited stable fluorescence, good biocompatibility, and a fluorescence lifetime sensitive to nucleic acids (DNA and RNA). The as-prepared F-NCDs act as a probe to quantify and distinguish the distribution of DNA and RNA in the nucleus via multicolor imaging by two-photon fluorescence lifetime microscopy (TP-FLIM). The method was particularly effective in tracking changes in the DNA/RNA distribution in plant cell nuclei (onion root tips) during different division stages and distinguishing animal tissues (zebrafish). The development of F-NCDs provides insights into the preparation of two-photon carbon dots and offers an effective visualization tool for TP-FLIM to dynamically study the function of genetic material in various life activities.

Shape and Size Dependence of Pharmacokinetics, Biodistribution, and Toxicity of Gold Nanoparticles

Gold nanoparticles (AuNPs) are extensively utilized in biomolecular sensing, photothermal therapy, drug delivery, and various imaging techniques like photoacoustic and fluorescent imaging. Despite their diverse applications, inconsistent findings from previous toxicity studies underscore the critical need for standardized methodologies. This study introduces ten distinct types of AuNPs─cubes, stars, rods, dumbbells, and bipyramids at sizes of 50 and 100 nm, to systematically assess their toxicity under controlled conditions both in vitro and in vivo. Our findings reveal a clear correlation between cytotoxicity and the morphology, size, incubation duration, and concentration of AuNPs. Anisotropically shaped nanoparticles, such as nanorods, nanodumbbells, and nanobipyramids, tend to exhibit higher cytotoxicity compared to more spherical forms like nanocubes and nanostars. Interestingly, while in vivo plasma biochemistry parameters show minimal variation, biodistribution, histopathological alterations, and pharmacokinetics are notably influenced by the shape and size of AuNPs. In most instances, smaller and anisotropic AuNPs that remain in the bloodstream for extended periods are observed. This research offers significant insights into the design of AuNPs with specific morphologies and sizes, particularly for their application in drug delivery systems via intravenous injection. These outcomes emphasize the nuanced toxicity profiles of AuNPs, necessitating tailored approaches in preclinical and clinical research.

A self-powered theranostic DNA nanodevice for amplification of both intracellular microRNA imaging and photodynamic therapy

While numerous methods exist for diagnosing tumors through the detection of miRNA within tumor cells, few can simultaneously achieve both tumor diagnosis and treatment. In this study, a novel graphene oxide (GO)-based DNA nanodevice (DND), initiated by miRNA, was developed for fluorescence signal amplification imaging and photodynamic therapy in tumor cells. After entering the cells, tumor-associated miRNA drives DND to Catalyzed hairpin self-assembly (CHA). The CHA reaction generated a multitude of DNA Y-type structures, resulting in a substantial amplification of Ce6 fluorescence release and the generation of numerous singlet oxygen (1O2) species induced by laser irradiation, consequently inducing cell apoptosis. In solution, DND exhibited high selectivity and sensitivity to miRNA-21, with a detection limit of 11.47 pM. Furthermore, DND discriminated between normal and tumor cells via fluorescence imaging and specifically generated O21 species in tumor cells upon laser irradiation, resulting in tumor cells apoptosis. The DND offer a new approach for the early diagnosis and timely treatment of malignant tumors.

DNA Nanolock-Based Logic Gate-Directed Reciprocal Feedback for Stepwise Cell Typing and Combination Treatment

To achieve accurate molecular diagnosis and early-stage intervention of disease on demand, there is an urgent need for the monitoring of multiple biomarkers and multipath information acquisition in living cells. The DNA combinatorial logic gate is an appropriate strategy for providing a systematic proof of concept with comprehensive information and function. Herein, a modular DNA logic gate nanomachine is designed for sufficient multistep reciprocal cell identification and therapy via the iteration of simple logic operations. In this logic gate system, this main module is constructed by G-quadruplex-locked gold nanocages (AuNCs), serving dual functions of drug encapsulation and cell recognition. The logic system is composed of OR, XNOR, AND, and NOR gates employing two intracellular disease biomarkers (microRNA 21 and microRNA 155) as inputs and the fluorescence signal of doxorubicin (Dox) as an output. The output signals of the four logic gates are iterated to process the imaging analysis data from the complex matrix in the living cell. Via positive and negative reciprocal feedback, the series circuit of different gates enables different functions, including the preliminary screening and the distinction of the cell type. Through the mutual preliminary screening and further proof, this logic system achieves accurate identification of cells, controlled drug release, and photothermal treatment using the AuNC as a photothermal transducer. This DNA logic system broadens the applications of the biocomputing system in disease screening and logic-controlled treatment fields.

Functional structures assembled based on Au clusters with practical applications

The advancement of gold nanoclusters (Au NCs) has given rise to a new era in fabricating functional materials due to their controllable morphology, stable optical properties, and excellent biocompatibility. Assemblies based on Au NCs demonstrate significant potentiality in constructing multiple structures as acceptable agents in applications such as sensing, imaging technology, and drug delivery systems. In addition, the assembled strategies illustrate the integration mechanism between each component while facing material requirement. It is necessary to provide supplementary and comprehensive reviews on the assembled functional structures (based Au NCs), which hold promise for applications and could expand their functional range and potential applications. This review focuses on the assembled structures of Au NCs in combination with metals, metal oxides, and non-metal materials, which are intricately arranged through various interaction forces including covalent bonds and metal coordination, resulting in a diverse array of multifunctional Au NC assemblies. These assemblies have widespread applications in fields such as biological imaging, drug delivery, and optical devices. The review concludes by highlighting the challenges and future prospects of Au NC assemblies, emphasizing the importance of continued research to advance nanomaterial assembly innovation.

Rapid Glutathione Analysis with SERS Microneedles for Deep Glioblastoma Tissue Differentiation

Rapid tissue differentiation at the molecular level is a prerequisite for precise surgical resection, which is of special value for the treatment of malignant tumors, such as glioblastoma (GBM). Herein, a SERS-active microneedle is prepared by modifying glutathione (GSH)-responsive molecules, 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), on the surface of Au@Ag substrates for the distinction of different GBM tissues. Since the Raman signals on the surface of the DTNB@Au@Ag microneedle can be collected by both portable and benchtop Raman spectrometers, the distribution of GSH in different tissues at centimeter scale can be displayed through Raman spectroscopy and Raman imaging, and the entire analysis process can be accomplished within 12 min. Accordingly, in vivo brain tissues of orthotopic GBM xenograft mice and ex vivo tissues of GBM patients are accurately differentiated with the microneedle, and the results are well consistent with tissue staining and postoperative pathological reports. In addition, the outline of tumor, peritumoral, and normal tissues can be indicated by the DTNB@Au@Ag microneedle for at least 56 days. Considering that the tumor tissues are quickly discriminated at the molecular level without the restriction of depth, the DTNB@Au@Ag microneedle is promising to be a powerful intraoperative diagnostic tool for surgery navigation.

Recent Advances in Gold Nanocluster-Based Biosensing and Therapy: A Review

Gold nanoclusters (Au NCs) with bright emission and unique chemical reactivity characters have been widely applied for optical sensing and imaging. With a combination of surface modifications, effective therapeutic treatments of tumors are realized. In this review, we summarize the recently adopted biosensing and therapy events based on Au NCs. Homogeneous and fluorometric biosensing systems toward various targets, including ions, small molecules, reactive oxygen species, biomacromolecules, cancer cells, and bacteria, in vitro and in vivo, are presented by turn-off, turn-on, and ratiometric tactics. The therapy applications are concluded in three aspects: photodynamic therapy, photothermal therapy, and as a drug carrier. The basic mechanisms and performances of these systems are introduced. Finally, this review highlights the challenges and future trend of Au NC-based biosensing and therapy systems.