Quantum dots have been widely applied in biosensing due to their outstanding optical properties. The emissions of quantum dots are mainly determined by their composition and size, as described by the Brus’s equation. Somehow, in this case, their emissions are hardly regulated reversibly and responsively, which are unsuitable for biosensing and biodetection. In the last decade, capping ligands have been used for designing biosensors because of their responsive regulation on the photoluminescence of quantum dots. Here, we first summarize the advances in characterization and calculation specific for ligands, which have helped to provide insights into the photoluminescence process and energy band theory of quantum dots. We then review two ways of ligand design that influence the optical properties of quantum dots: affecting the process of photoluminescence, or the orbital/electronic structure. In the latter case, the atoms on both the ligand and the surface of the quantum dot interact to affect the energy band structure of the quantum dot core. Examples are presented of how these quantum dots that possess responsive properties due to the design of the ligands have been applied to sensing. With further exploration, we hope to see advances in the fundamental understanding of the energy band structures and practical applications of these quantum dots.
Membrane proteins are vital components of the cell membrane and play crucial roles in various cellular activities. Analysis of membrane proteins is of paramount importance for studying molecular events inside cells and organisms and holds promising prospects for early disease diagnosis and treatment assessment. Benefiting from obvious merits including high affinity, high specificity and ease of modification, aptamers have been regarded as ideal molecular recognition elements in membrane protein analysis and molecular diagnostics strategies. This review summarised recent advances in membrane protein-specific aptamer screening, aptamer-based static and dynamic membrane protein analysis, and aptamer-based molecular diagnostic techniques. Prospects and challenges were also discussed.
The small-molecule fluorophores for the second near-infrared (NIR-II, 1000–1700 nm) window have attracted increasing attention in basic scientific research and preclinical practice owing to their deep-photo penetration, minimal physiological toxicity and simplicity of chemical modification. However, most of the reported small-molecule NIR-II fluorophores suffered from poor water solubility, which can easily cause organ toxicity. In addition, the aggregation caused by their poor water solubility in the aqueous solution would also result in weak fluorescence of these NIR-II fluorophores. Thus, it is highly desirable and valuable to develop water-soluble small-molecule NIR-II fluorophores with excellent photophysical properties for high-contrast in vivo imaging. In this review, we summarize the recent research advances in water-soluble small-molecule NIR-II fluorophores and highlight the representative bioimaging applications. Moreover, the potential challenges and perspectives of water-soluble small-molecule NIR-II fluorophores are discussed as well. We anticipate this review can help researchers to grab the latest information of water-soluble small-molecule fluorophores for NIR-II imaging, sequentially boosting their further development.
Cancer is a leading cause of death worldwide, and a series of strategies has been reported for tumor-specific therapy. Currently, chemodynamic therapy (CDT) has become a research hotspot for antitumor treatment due to its advantages of high specificity, endogenous stimulation, and high biosafety. However, the therapeutic effects of CDT are normally limited in the complex tumor microenvironment (TME), such as insufficient acidity, tumor hypoxia, low hydrogen peroxide (H2O2), and high glutathione (GSH). Consequently, different kinds of multifunctional nanomaterials have been designed to manipulate TME conditions, which provided more opportunities to improve the efficiency of CDT. This review focuses on nanomaterial-based strategies for enhancing CDT through manipulating TME. Upon CDT enhancements, this review would provide a reference for the future development of efficient CDT nanomaterials.
Accurate detection of biomarkers is essential for disease diagnosis. Although the highly sensitive fluorescence probes are feasible for the above goal, it is typically interfered by the auto-fluorescence and light scattering of the biological samples. Photochemical afterglow system (consisting of photosensitizer, afterglow substrate and emitter) based on cascade photochemical reactions exhibits long-lived luminescence (seconds to hours), thus avoiding background interference. With the assistance of polymers, such as polystyrene microspheres, the photochemical afterglow systems have been transformed into homogeneous and water-soluble nanoparticles, and used for in-vitro biomarker analysis. Here, we summarized the principle, preparation and applications of these afterglow nanoparticles, and evaluated their performance in clinical sample testing by comparing with other nanoparticle-based methods. Finally, several problems and possible solutions of afterglow nanoparticle-based methods in biomarker determination were also mentioned.
Cysteine is an important regulator of redox processes. Due to the nucleophilic and oxidative sensitivity, cysteine residues in proteins can be oxidized by intracellular reactive oxygen species (ROS), which can lead to protein structural and functional changes. Hence, the development of fluorescent probes to image cysteine and cysteine oxidation is of great significance for the study of redox homeostasis in living system. In this review, the development of fluorescent probes for imaging cysteine and cysteine oxidation was summarized. Moreover, we further analyzed defects of the reported fluorescent probes and made suggestions for the future development of fluorescent probes. We expect that this review can not only provide a deeper understanding of the role of cysteine and cysteine oxidation in oxidative stress, but also broaden the application of fluorescent probes in imaging cysteine and cysteine oxidation.
Exosomes, extracellular vesicles (EVs) that play crucial roles in biological processes, have emerged as attractive targets for noninvasive disease diagnosis and monitoring. Mass spectrometry (MS) offers high sensitivity, high throughput, and excellent qualification and quantification capacity, which is the ideal approach for exosome analysis. Nanomaterials’ unique physiochemical properties, controllable morphology, and large surface area make them promising in biological sample pretreatment and detection. They contributed diverse functions to the exosome MS analysis, encompassing substrates for exosome isolation and cargos enrichment, matrices for laser desorption/ionization (LDI), read-out signals and supporters for signal amplification strategies, etc. In this review, recent progress in the applications of nanomaterial in the exosome MS analysis was summarized and a comprehensive discussion on the challenges and perspectives was proposed for the development of an advancing analysis approach of exosomes for the accurate diagnosis and monitoring of diseases.
The cell membrane is a critical barrier for cellular homeostasis, integral to signaling and intercellular communication, and vital for understanding cellular functions and disease mechanisms. Investigating its microenvironment is crucial for uncovering the molecular basis of physiological and pathological processes associated with the cell membrane, driving the development of bioanalytical toolkits capable of dynamically monitoring the cell surface microenvironment. With the continuous advancement of functional nucleic acids and dynamic DNA nanotechnology, DNA nanodevices with controllable nanosized geometry, specific molecular recognition, and selective membrane-localization properties offer a versatile platform for probing the cell membrane microenvironment. In this review, we summarize the current biosensing and membrane-anchoring mechanisms of DNA nanodevices and highlight their use in studying key cell membrane events, including membrane lipid dynamics, transmembrane transport, receptor dimerization, and signal transduction. Furthermore, we discuss the challenges and potential future applications of DNA nanodevices in advancing cell membrane biology research and biomedical applications.
Nanopore-based electrochemical technique is a promising tool for detecting single proteins. However, detecting single proteins using a nanopipette in their native state without labeling is challenging due to the rapid translocation, which results in an inefficient signal identification. In our study, we finely tuned the driving force equilibrium between electrophoretic force (EPF) and electroosmotic flow (EOF) inside the nanopipette for efficient sensing of single glucose oxidase (GOD) molecules. The duration time of GOD within the nanopipette is extended to about 4 ms. This strategy provided clear ionic current signals with a signal-to-noise ratio of 3.3. As EPF increased in the direction opposite to the motion of GOD, we observed a nonlinear growth in GOD’s duration time. This extended the duration to about 4.4 times longer at −1000 mV compared to at −800 mV. Hence, nanopore-based electrochemical sensing could be used for single GOD molecule analysis as an ultrasensitive method.
Here we employ in-situ UV-Vis spectroscopy to monitor the sulfur redox reaction with oxygen-containing molecules as an additive, for example, biphenyl-4,4′-dicarboxylic acid (BDC). Furthermore, Raman spectrum, electron paramagnetic resonance (EPR), and electrospray ionization-mass spectrometry (ESI-MS) measurements reveal that the formation of BDC-S3 •‒ complexes can establish the long-term stability of polysulfide radicals, change the kinetics of sulfur redox reaction, and then generate decent capacity retention and rate capability. According to the density functional theory (DFT) analysis, S3 •‒ radicals are the underlying product of S6 2‒ cleavage, owing to the decreased chemical energy and the increased stability of S3 •‒ radicals through Lewis acid-base interaction. The assembled Li-S batteries with BDC additive deliver a high reversible capacity of 420 mA·h·g−1 over 200 cycles with over 98% Coulombic efficiency, under the current density of 0.2 C.
Intracellular pH (pHi) is a fundamental indicator of cellular physiological state, regulating cellular state and function, and has important research values. Although various probes for measuring intracellular pH were available, it is challenging to reflect pHi in real-time and reversible manners. Herein, we developed a whole-cell bioluminescent (BL) probe based on wild type BL bacteria, photobacterium phosphoreum (P. phosphoreum), to determine and image pHi. The dependence of BL intensity of P. phosphoreum on pH values of culture solutions was established. It was found that BL intensity could respond to the change of pH values rapidly and reversibly. We further revealed that P. phosphoreum maintained pH homeostasis in the extracellular pH (pHe) within the range of 5.0–7.0, while intracellular pH homeostasis was destroyed at the alkaline pHe. This method opens up the enormous potential of BL bacteria as an alternative to fluorescence for monitoring and imaging pHi.
The combination of near-infrared (NIR) fluorescence imaging (FLI) and photoacoustic imaging (PAI) can effectively compensate for each other’s inherent limitations, which can provide reliable and rich information on tumor biology. Therefore, the development of FL/PA dual-modality imaging probes is beneficial for achieving precision cancer diagnosis and treatment. Herein, we designed an efficient phototherapy agent methoxy bithiophene indene (OTIC), which was based on aggregation-induced emission (AIE) active fluorophores. To improve the water dispersion and enrichment of OTIC at the tumor site, OTIC nanoparticles (OTIC NPs) were prepared by a nanoprecipitation method. The balance between radiation and non-radiation energy dissipation was regulated by the strong donor-acceptor interaction and intramolecular motion. So OTIC NPs exhibited bright NIR fluorescence, photoacoustic signals, efficient generation of reactive oxygen species, and high photothermal conversion efficiency under NIR irradiation. Accurate imaging of the tumor and mice sentinel lymph nodes (SLNs) with OTIC NPs was visualized by NIR FL/PA dual-modal imaging. With the comprehensive imaging information provided by OTIC NPs in vivo, tumors were ablated under laser irradiation, which greatly improved the therapeutic efficacy. OTIC NPs would be possible to realize the precise guidance of FL/PA imaging for tumor treatment in the future clinical application.
The insufficient internal resorption of iodide ions (I−) leads to thyroid disorders, such as goiter, hypothyroidism, and cretinism in adults. In this paper, a portable point-of-care testing (POCT) platform was developed for the dual-modal analysis of I−, seamlessly integrating both colorimetric and photothermal thermometer techniques. The quantification of results was achieved using a standard thermometer or smartphone. G-Quadruplex/Hemin (G4/Hemin) is the DNAzyme with peroxidase-like activity. The catalytic efficacy of G-quadruplex structures can be enhanced with the help of I−, manifesting as multicolor transitions from colorless to green and then blue, and accompanied by the increase of temperature, which can be used for the quantitative detection of I−. Additionally, digital analysis according to the three-color channels (R/G/B) by a cellphone eliminated the requirement for intricate instruments. This dual-modal method for portable I− determination is cost-effectiveness, simplicity, remarkable sensitivity (0.5 nmol/L) and selectivity. Besides, it was applied to determining the concentration of I− in spiked serum samples.
Small gold nanorods (AuNRs), namely AuNRs with less than 10 nm in diameter, possess a high absorption-to-scattering ratio, a large surface area-to-volume ratio, as well as high cellular uptake behaviors. In this study, we systematically investigate seedless synthesis of AuNRs with diameters ranging from 5 nm to 10 nm. It has been found that several experimental conditions, including the chain length of the used cationic surfactants, and the concentrations of ascorbic acid, NaBH4, and AgNO3 can profoundly affect the obtained products. Under optimal conditions, the production yields of the obtained several AuNRs with different diameters can exceed 90% and even reach almost 100%. The conversion of gold precursors to AuNRs was estimated to be 70%–77% as measured by absorption spectroscopy and inductively coupled plasma mass spectrometry.
Acid phosphatase (ACP) is a ubiquitous phosphatase in living organisms. The abnormal variation of ACP is related to various diseases. Herein, we propose a colorimetric method based on CeO2-modified gold core shell nanoparticles (Au@CeO2 NPs) to analyze ACP activity with high sensitivity and specificity. In this design, 2-phospho-L-ascorbic acid trisodium salt (AAP) is dephosphorylated by ACP and produces reductive ascorbic acid (AA), which makes the CeO2 shell decomposition. A remarkable blue shift of localized surface plasmon resonance peak (LSPR, from yellow to green) along with the scattering intensity ratio changes from individual Au@CeO2 NPs are observed. ACP activity can be quantified by calculating the ratio changes of individual Au@CeO2 NPs. This assay reveals limit of detection (LOD) of 0.044 mU/mL and the linear range of 0.05–5.0 mU/mL, which are much lower than most of spectroscopic measurements in bulk solution. Furthermore, the recovery measurements in real samples are satisfactory and the capacity for practical application is demonstrated. As a consequence, Au@CeO2 NPs used in this assay will find new applications for the ultrasensitive detection of enzyme activity.
Nanochannels have made great progress and are a promising platform for detecting a series of targets. However, most nanochannels are modified on the inner wall, while ignoring the outer surface. Here, we modified the outer surface of nanochannels with hydrogel. Different from other reported outer-surface modification methods, we directly cover nanochannels with hydrogel to form heterogeneous membrane. The selected hydrogel hardly adsorbs other ions and shows specific adsorption for Cr(VI). The adsorption sites in hydrogel are homogeneous, and Cr(VI) adsorption onto hydrogel is endothermic and spontaneous. The charge in hydrogel changes after Cr(VI) adsorption, and the resulting current changes can be used for the detection of Cr(VI) with the detection limit of 10−11 mol/L. Our platform is expected to be used for Cr(VI) detection in living organisms, especially within cells. This work provides a new approach for outer-surface modification of nanochannels and offers a new choice for nanochannel detection platforms.
In molecular engineering, designing and synthesizing molecular machines with capable of performing complex tasks, remains a formidable challenge. DNA is an excellent candidate for building molecular robots because it is highly programmable. Here, we present an artificial nanorobot, in which a DNA cube serves as the inert ‘body’, and nucleic acid catalysts based on an enzymatic nicking reaction act as the ‘legs’ for walking. The nanorobot can execute a series of actions, such as ‘start’, ‘turn’, and ‘stop’ when it walks along a predefined track. Its performance could be confirmed and monitored by using an atomic force microscope (AFM) and fluorescence spectroscopy. Inspired by biological machines, we artificially designed a series of specialized tasks that combined walking with control of cargo transport and catalysis. Real-time fluorescence kinetics curves provide monitoring signals for cargo transport and catalytic processes. Our work can enrich the toolbox of DNA machinery and has great potential for engineering molecular nanofactories.