General Sensitive Detecting Strategy of Ions through Plasmonic Resonance Energy Transfer from Gold Nanoparticles to Rhodamine Spirolactam

Methylmercury-sensitized "turn on" SERS-active peroxidase-like activity of carbon dots/Au NPs nanozyme for selective detection of ochratoxin A in coffee

The improvement and regulation of catalytic performance of nanozyme have long been pursued with sustained efforts. Herein, gold nanoparticles (S-CDs/AuNPs) with weak peroxidase-like (POD) activity were synthesized by Au-S bond using a sulfur doped carbon dots (S-CDs) as reducing agent and stabilizer. However, methylmercury (MeHg+) could selectively and sensitively regulate the POD-like activity of S-CDs/AuNPs. The catalytic activity of S-CDs/AuNPs was significantly activated with the addition of MeHg+, resulting in a significant enhancement of electromagnetic fields to present an obvious SERS signal. More intriguingly, the introduction of ochratoxin A (OTA) could simultaneously turn off the UV-vis absorbance signals and the surface-enhanced Raman scattering (SERS) signal. Based on these findings, a selective colorimetric-SERS dual-mode OTA detection strategy was established with gold amalgamation (Au@HgNPs) as the probe, and the low limit of detection (LOD) of OTA was 0.29 µgL-1 (Colorimetric) and 0.16 µgL-1 (SERS), respectively, with good recoveries from 95.9 to 104.0% (Colorimetric) and from 96.7 to 108.9% (SERS), respectively. The work paves a new way to design nanozyme-based colorimetric and SERS protocol for traces OTA residues analysis in foodstuff analysis.

Fluorogen-Functionalized Mesoporous Silica Hybrid Sensing Materials: Applications in Cu2+ Detection

Since Cu2+ ions play a pivotal role in both ecosystems and human health, the development of a rapid and sensitive method for Cu2+ detection holds significant importance. Fluorescent mesoporous silica materials (FMSMs) have garnered considerable attention in the realm of chemical sensing, biosensing, and bioimaging due to their distinctive structure and easily functionalized surfaces. As a result, numerous Cu2+ sensors based on FMSMs have been devised and extensively applied in environmental and biological Cu2+ detection over the past few decades. This review centers on the recent advancements in the methodologies for preparing FMSMs, the mechanisms underlying sensing, and the applications of FMSMs-based sensors for Cu2+ detection. Lastly, we present and elucidate pertinent perspectives concerning FMSMs-based Cu2+ sensors.

Principles and Applications of Resonance Energy Transfer Involving Noble Metallic Nanoparticles

Over the past several years, resonance energy transfer involving noble metallic nanoparticles has received considerable attention. The aim of this review is to cover advances in resonance energy transfer, widely exploited in biological structures and dynamics. Due to the presence of surface plasmons, strong surface plasmon resonance absorption and local electric field enhancement are generated near noble metallic nanoparticles, and the resulting energy transfer shows potential applications in microlasers, quantum information storage devices and micro-/nanoprocessing. In this review, we present the basic principle of the characteristics of noble metallic nanoparticles, as well as the representative progress in resonance energy transfer involving noble metallic nanoparticles, such as fluorescence resonance energy transfer, nanometal surface energy transfer, plasmon-induced resonance energy transfer, metal-enhanced fluorescence, surface-enhanced Raman scattering and cascade energy transfer. We end this review with an outlook on the development and applications of the transfer process. This will offer theoretical guidance for further optical methods in distance distribution analysis and microscopic detection.

Zinc-Carnosine Metallodrug Network as Dual Metabolism Inhibitor Overcoming Metabolic Reprogramming for Efficient Cancer Therapy

The targeting of tumor metabolism as a novel strategy for cancer therapy has attracted tremendous attention. Herein, we develop a dual metabolism inhibitor, Zn-carnosine metallodrug network nanoparticles (Zn-Car MNs), which exhibits good Cu-depletion and Cu-responsive drug release, causing potent inhibition of both OXPHOS and glycolysis. Notably, Zn-Car MNs can decrease the activity of cytochrome c oxidase and the content of NAD⁺, so as to reduce ATP production in cancer cells. Thereby, energy deprivation, together with the depolarized mitochondrial membrane potential and increased oxidative stress, results in apoptosis of cancer cells. In result, Zn-Car MNs exerted more efficient metabolism-targeted therapy than the classic copper chelator, tetrathiomolybdate (TM), in both breast cancer (sensitive to copper depletion) and colon cancer (less sensitive to copper depletion) models. The efficacy and therapy of Zn-Car MNs suggest the possibility to overcome the drug resistance caused by metabolic reprogramming in tumors and has potential clinical relevance.

Dual-Mode Optical Sensor Array for Detecting and Identifying Perillaldehyde in Solution Phase and Plant Leaf with Smartphone

Promising techniques for detecting and quantifying active components in the plants and foods have received global concern in smart agriculture. Dual-mode optical assays are becoming more attractive and popular thanks to robust and reliable analysis parameters. We herein unveil a novel turn-on and dual-mode sensor array comprising three kinds of reactive indicators including ring-closed rhodamine-hydrazine, squaraine-hydrazine, and 2,4-dinitrophenylhydrazine for evaluating perillaldehyde. Significant colorimetric and fluorescent changes were triggered through reacting primary amine/hydrazine with the active aldehyde group in perillaldehyde, thus turning on the chromogenic responses of all the indicators. Optimal colorimetric sensing showed good responses to perillaldehyde ranged up to 100 mM in ethanol. Dramatic fluorescence enhancement was also exhibited, illustrating good selectivity as well as high sensitivity (detection limit ∼20.0 μM). Inspired by rapid chemical reactions and distinct optical changes, distinct sensor array strips loaded with the optimal solid-state reactive indicators were developed for evaluating the perillaldehyde content in the perilla frutescence leaves. Smartphone-enabled readout system and digital data processing were further performed for chemometric analysis. A good correlation was obtained and the semiquantitative evaluation of the perillaldehyde content could be achieved within 15 min, possessing the significant features of naked-eye recognition, easy operation, and disposability. To the best of our knowledge, present work demonstrated the use of chromogenic sensing strips to evaluate the active perillaldehyde content in solution and vapor phases for the first time. Taken together, these characteristics also indicate that the present turn-on sensor array has great potential applications in the precise detection and evaluation of perillaldehyde in the forthcoming smart agriculture.

The precise modification of nanoscaled Keplerate-type polyoxometalate with NH2-groups: reactive sites, mechanisms and dye conjugation

The interaction of alkoxysilanes with nanoscaled giant polyoxoclusters is a challenging route for efficiently building blocks for supramolecular smart-tune design. 3-aminopropyltrimethoxysilane (APTMS) treatment grafts amino groups onto the surface of...

Transpeptidation-mediated single-particle imaging assay for sensitive and specific detection of sortase with dark-field optical microscopy

Transpeptidation of surface proteins catalyzed by the transpeptidase sortase plays a critical role in the infection process of Gram-positive pathogen. Monitoring sortase activity and screening its inhibitors are of great significance to fundamental understanding of the infection mechanism and pharmaceutical development. Herein, we developed a digital single-particle imaging method to quantify sortase A (SrtA) activity based on transpeptidation-mediated assembly and enumeration of gold nanoparticles (GNPs). The assay utilizes two peptide stands, in which one has the SrtA recognition sequence LPXTG motif while the other carries an oligoglycine nucleophile at the one end and a biotin group at the other. The presence of SrtA enables the ligation of two peptides and allows for the immobilization of streptavidin-functionalized GNPs. Thus, SrtA activity can be quantified by imaging and enumeration of the surface-assembled GNPs at the single-particle level via dark-field microscopy. The single-particle method was highly sensitive to SrtA activity with a low detection limit of 7.9 pM and a wide linear dynamic range from 0.05 to 50 nM. Besides detection of SrtA in complex biological samples such as Gram-positive pathogen lysates, the proposed method was also successfully applied to estimate the half-maximal inhibitory concentration (IC₅₀) values of SrtA inhibitors (curcumin, berberine hydrochloride and quercetin). The present method, combining single-GNP counting and dark-field imaging, provides a facile and novel analytical tool for SrtA activity and its inhibitor screening.

Nanosurface energy transfer indicating Exo III-propelled stochastic 3D DNA walkers for HIV DNA detection

DNA-based nanomachines have aroused tremendous interest because of their potential applications in bioimaging, biocomputing, and diagnostic treatment. Herein, we constructed a novel exonuclease III-propelled and signal-amplified stochastic DNA walker that autonomously walked on a spherical particle-based 3D track through a burnt-bridge mechanism, during which nanosurface energy transfer (NSET) occurred between the fluorescent dye modified on hairpin DNA and the surface of gold nanoparticles (AuNPs). As a proof of concept, this stochastic DNA walker achieves prominent detection performance of HIV DNA in the range of 0.05-1.2 nM with a detection limit of 12.7 pM and satisfactory recovery in blood serum, showing high promise in biosensing applications with complicated media.

Microwave-mediated fabrication of silver nanoparticles incorporated lignin-based composites with enhanced antibacterial activity via electrostatic capture effect

Lignin has been considered as a green carrier with excellent biocompatibility for the biomedical applications in drug release, tissue engineering, etc. In this study, silver nanoparticles (AgNPs) incorporated quaternized lignin (QAL) composites (Ag@QAL) were synthesized in-situ with the assistance of the microwave radiation. The positive charged QAL, not only serves as reductive and stabilizing carriers, but also endows with electrostatic effect toward negatively charged Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), resulting in greatly enhanced antibacterial activity. It is worth mentioning that Ag@QAL exhibits the highest antibacterial activity, which causes 3.72 log₁₀ (>99.9%) and 5.29 log₁₀ (>99.999%) CFU/ml reduction against E. coli and S. aureus respectively after contacting for only 5 min. Furthermore, due to the strong interaction between Ag@QAL and Ag⁺/AgNPs, bacteria can be captured and co-precipitated by Ag@QAL fastly in 30 min with almost none silver ions detected in the supernatant, which prevents Ag⁺ leaking with extremely low toxicity to the biological environment. This concept of electrostatic capture effect induced antibacterial activity enhancement and environmentally benign features may provide new insights into the design of highly effective antibacterial agents in a sustainable manner.

"Loading-type" Plasmonic Nanoparticles for Detection of Peroxynitrite in Living Cells

To date, plasmon resonance energy transfer (PRET)-based analytical approaches still inevitably suffer from limitations, such as lack of appropriate acceptor-donor pairs and the extra requirements of active groups of acceptors, which place great obstacles in extending the application of such methods, especially in the area of living cell studies. Herein, we design and fabricate a kind of "loading-type" plasmonic nanomaterials constituting gold nanoparticles as donors of PRET coated with mesoporous silicon, in which organic small molecules (CHCN) as acceptors of PRET were loaded (Au@MSN-CHCN). This "loading-type" strategy could conveniently integrate acceptor-donor pairs into one nanoparticle, so as to achieve the goal of sensitive detection of biomolecules in a complex physiological microenvironment. Based on the change of PRET efficiency of Au@MSN-CHCN induced by the specific reaction between CHCN and peroxynitrite (ONOO^-), ONOO^-, which plays an irreplaceable role in a series of physiological and pathological processes, is sensitively and selectively detected. Furthermore, in situ imaging of exogenous and endogenous ONOO^- in living cells was achieved even at a single nanoparticle level. This work provides a general approach to construct PRET probes for visualizing various biomolecules in living cells.

Organocatalytic Synthesis of α-Triphenylmethylamines from Diarylketimines and Phenols

A formal Betti reaction between variously substituted phenols and benzophenone-derived imines to afford α-triphenylmethylamines is reported. The key to the success of this transformation is the in situ generation of the reactive benzophenone iminium species under organocatalytic conditions. Different phenols reacted smoothly, enabling the synthesis of an array of α-triphenylmethylamines, which are highly valued structural motifs in bioactive molecules and chemical sensors.

Boosting Visible-Light Photocatalytic Redox Reaction by Charge Separation in SnO2 /ZnSe(N2 H4 )0.5 Heterojunction Nanocatalysts

In this work, environmentally friendly photocatalysts with attractive catalytic properties are reported that have been prepared by introducing SnO2 quantum dots (QDs) directly onto ZnSe(N2 H4 )0.5 substrates to induce advantageous charge separation. The SnO2 /ZnSe(N2 H4 )0.5 nanocomposites could be easily synthesized through a one-pot hydrothermal process. Owing to the absence of capping ligands, the attached SnO2 QDs displayed superior photocatalytic properties, generating many exposed reactive surfaces. Moreover, the addition of a specified amount of SnO2 boosted the visible-light photocatalytic activity; however, the presence of excess SnO2 QDs in the substrate resulted in aggregation and deteriorated the performance. The spectroscopic data revealed that the SnO2 QDs act as a photocatalytic mediator and enhance the charge separation within the type II band alignment system of the SnO2 /ZnSe(N2 H4 )0.5 heterojunction photocatalysts. The separated charges in the heterojunction nanocomposites promote radical generation and react with pollutants, resulting in enhanced photocatalytic performance.

Selective Ultrasensitive Optical Fiber Nanosensors Based on Plasmon Resonance Energy Transfer

The facet of optical fibers coated with nanostructures enables the development of ultraminiature and sensitive (bio)chemical sensors. The sensors reported until now lack specificity, and the fabrication methods offer poor reproducibility. Here, we demonstrate that by transforming the facet of conventional multimode optical fibers onto plasmon resonance energy transfer antenna surfaces, the specificity issues may be overcome. To do so, a low-cost chemical approach was developed to immobilize gold nanoparticles on the optical fiber facet in a reproducible and controlled manner. Our nanosensors are highly selective as plasmon resonance energy transfer is a nanospectroscopic effect that only occurs when the resonance wavelength of the nanoparticles matches that of the target parameter. As an example, we demonstrate the selective detection of picomolar concentrations of copper ions in water. Our sensor is 1000 times more sensitive than the state-of-the-art technologies. An additional advantage of our nanosensors is their simple interrogation; it comprises of a low-power light-emitting diode, a multimode optical fiber coupler, and a miniature spectrometer. We believe that the plasmon resonance energy transfer-based fiber-optic platform reported here may pave the way for the development of a new generation of ultraminiature, portable, and hypersensitive and selective (bio)chemical sensors.

A fluorescence imaging protocol for correlating intracellular free cationic copper to the total uptaken copper by live cells

A variety of fluorescence probes have been developed for fluorescence imaging of metals in biological cells. However, accurate quantification of metals with fluorescent approaches is challenging due to the difficulty in establishing a standard calibration curve in living cells. Herein, a fluorescence imaging protocol is developed for imaging intracellular Cu²⁺ and its correlation with the cellular uptake of copper. The total amount of intracellular Cu is detected by inductively coupled plasma mass spectrometry (ICP-MS) in parallel. Fluorescence imaging of Cu²⁺ is accomplished with Rhodamine B derivative modified carbon dots (CDs-Rbh) based on fluorescence resonance energy transfer (FRET) from CDs to rhodamine. Intracellular Cu²⁺ is correlated with fluorescence ratio at λ_em 500-600 nm (rhodamine) to λ_em 425-475 nm (CDs) with excitation at λ_ex 405 nm. It is found that Cu²⁺ is linearly correlated with the total intracellular uptaken copper content, with a linear correlation between the relative fluorescence ratio in fluorescence imaging and intracellular Cu derived from ICP-MS, including both Cu(I) and Cu(II) species. The linear calibration equation is lg(F₂/F₁) = 0.00148 m[Cu]-0.3622. This approach facilitates further investigation and elucidation of copper transition in live cells and the evaluation of their cytotoxicity.

Combined Use of Anisotropic Silver Nanoprisms with Different Aspect Ratios for Multi-Mode Plasmon-Exciton Coupling

Absorption enhancement based on interaction between the localized surface plasmon (LSP) and molecular exciton is one of the most important phenomena for the development of high-performance solar devices. In this study, hybrids of plasmonic metal nanoparticles and dye molecules have been developed, which exhibit enhanced absorption at precisely tuned wavelengths in a visible region. The hybrids consist of a porphyrin derivative, which has four absorption peaks (Q-bands) in a range of 500-700 nm, and triangular silver nanoprisms (AgPRs), which are developed by us to exhibit precisely tuned LSP resonance wavelengths. Absorption enhancement over the whole Q-band range is induced by the combined use of three kinds of AgPRs of different aspect ratios. Furthermore, the quantitative evaluation of absorption enhancement based on the LSP-based fluorescence enhancement phenomenon has demonstrated that efficient absorption enhancement can be effected at multiple wavelengths.

Plasmonic resonance energy transfer from a Au nanosphere to quantum dots at a single particle level and its homogenous immunoassay

PRET from a AuNS to a QD is discovered at a single particle level, and then is used to develop ultra-sensitive homogenous immunoassays.

A single gold nanoprobe for colorimetric detection of silver(i) ions with dark-field microscopy

In this work, the formation of C–Ag⁺–C bonding between cytosines was utilized to induce interparticle coupling of gold nanoparticles modified with single-strand DNA, resulting in a color change as the signal transduction to quantify Ag⁺ sensitively under dark-field microscopy imaging, while we achieved the quantification of Ag⁺ could be directly realized in lake water samples and drug samples.

Plasmon Coupling Effect-Enhanced Imaging of Metal Ions in Living Cells Using DNAzyme Assembled Core-Satellite Structures

We demonstrate a core-satellite plasmonic nanoprobe assembled via metal-ion-dependent DNA-cleaving DNAzyme linker for imaging intercellular metal ion based on plasmon coupling effect at a single-particle level. As metal ions are present in the system, the DNAzyme linker will be cleaved, and thus, disassembly of the core-satellite nanoprobes occurs, which results in distinct blue shift of the scattering spectra of Au core-satellite probes and naked color change of the scattering light. This change in scattering spectra has been supported by theoretical simulations. As a proof of concept, sensitive detection of Cu²⁺ with a limit of detection down to 67.2 pM has been demonstrated. The nanoprobes have been further utilized for intracellular Cu²⁺ imaging in living cells. The results demonstrate that the present strategy provides a promising platform for detection and imaging of metal ions in living cells and could be potentially applied to imaging other interesting target molecules simply by substituting the oligonucleotide sequence.

Surface-engineered quantum dots/electrospun nanofibers as a networked fluorescence aptasensing platform toward biomarkers

A membrane-based fluorescent sensing platform is a facile, point-of-care and promising technique in chemo/bio-analytical fields. However, the existing fluorescence sensing films for cancer biomarkers have several problems, with dissatisfactory sensitivity and selectivity, low utilization of probes encapsulated in films as well as the tedious design of membrane structures. In this work, a novel fluorescence sensing platform is fabricated by bio-grafting quantum dots (QDs) onto the surface of electrospun nanofibers (NFs). The aptamer integrated into the QDs/NFs can result in high specificity for recognizing and capturing biomarkers. Partially complementary DNA-attached gold nanoparticles (AuNPs) are employed to efficiently hybridize with the remaining aptamer to quench the fluorescence of QDs by nanometal surface energy transfer (NSET) between them both, which are constructed for prostate specific antigen (PSA) assay. Taking advantage of the networked nanostructure of aptamer-QDs/NFs, the fluorescent film can detect PSA with high sensitivity and a detection limit of 0.46 pg mL^-1, which was further applied in real clinical serum samples. Coupling the surface grafted techniques to the advanced network nanostructure of electrospun NFs, the proposed aptasensing platform can be easily extended to achieve sensitive and selective assays for other biomarkers.