Fluorescent Nanoswitch Research Articles

Fluorescent nanoswitch based on redox-controlled reversible sulfhydryl functionalized carbon dots for highly sensitive detection of ochratoxin A

In this work, sulfhydryl functionalized carbon dots (SH-CDs) were synthesized for the first time by a two-step hydrothermal method. The sulfhydryl group in SH-CDs can be converted efficiently and reversibly in a few minutes under redox conditions. On this basis, ochratoxin A (OTA) induced hybrid chain reaction amplification and alkaline phosphatase enzymatic hydrolysis to produce ascorbic acid (AA). AA reduced the aggregated SH-CDs, thereby realizing the dual-mode rapid quantitative analysis of the OTA concentration by measuring the changes in the fluorescence intensity and absorbance of the SH-CDs solution. The proposed sensor has a good linear relationship with the OTA concentration in the range of 2.0–5.0 nM, and the lowest detection limit is 2.0 nM. Additionally, the visual color change of the solution can improve the simplicity and accuracy of semi-quantitative detection of OTA with the naked eye. In short, this method has the advantages of rapidity, sensitivity, reversibility and visualization.

Programmable molecular circuit discriminates multidrug-resistant bacteria.

Recognizing multidrug-resistant (MDR) bacteria with high accuracy and precision from clinical samples has long been a difficulty. For reliable detection of MDR bacteria, we investigated a programmable molecular circuit called the Background-free isothermal circuital kit (BRICK). The BRICK method provides a near-zero background signal by integrating four inherent modules equivalent to the conversion, amplification, separation, and reading modules. Interference elimination is largely owing to a molybdenum disulfide nanosheets-based fluorescence nanoswitch and non-specific suppression mediated by molecular inhibitors. In less than 70 ​min, an accurate distinction of various MDR bacteria was achieved without bacterial lysis. The BRICK technique detected 6.73 ​CFU/mL of methicillin-resistant Staphylococcus aureus in clinical samples in a proof-of-concept trial. By simply reprogramming the sequence panel, such a high signal-to-noise characteristic has been proven in the four other superbugs. The proposed BRICK method can provide a universal platform for infection surveillance and environmental management thanks to its superior programmability.

Multifunctional Carbon Dots for Trace Water Detection, White LEDs, and Bioimaging

AbstractHighly fluorescent, ultrafine CDs were synthesized by a simple one‐pot solvothermal method. The as‐prepared CDs exhibited unique yellow emission and intrinsic fluorescence characteristics independent of excitation wavelengths. We revealed a distinct fluorescence quenching mechanism in the CDs, where the reversible alternation between aggregation and dispersion states can mediate the fluorescence turn‐on and turn‐off response. Therefore, the CDs can be used as a fluorescence nanoswitch for the highly sensitive quantitative detection of trace water in organic solvents. We also demonstrated the applications of the CDs as a stable yellow phosphor and biological probe for white LEDs and biomembrane imaging. Our results suggest that the low‐cost fluorescent material has great promise for practice applications in sensing, bioimaging, and optoelectronic device.

Zinc ion-triggered aggregation induced emission enhancement of dual ligand co-functionalized gold nanoclusters based novel fluorescent nanoswitch for multi-component detection

Herein, a zinc ion (Zn2+)-triggered aggregation induced emission enhancement (AIEE) fluorescence “on-off-on” nanoswitch was fabricated for inorganic pyrophosphate (PPi) and inorganic pyrophosphatase (PPase) activity detection. Dual ligand functionalized Au NCs were utilized as the substrate of the AIEE nanoswitch. The introduction of Zn2+ can cause Au NCs aggregated along with the enhanced fluorescence. After the addition of PPi, aggregated Au NCs disaggregated along with decreased fluorescence due to the competitive combination between PPi and Zn2+ (on-off). When PPase was introduced, PPi was hydrolyzed and release Zn2+, resulting in aggregated Au NCs along with enhanced fluorescence again (off-on). On the basis of this, highly selective and sensitive detection PPi (liner range from 0.1 to 300 μM) and PPase activity (liner range from 0.1 to 10 mU) can be achieved. The detection limits are 0.04 μM for PPi and 0.03 mU for PPase, respectively. Furthermore, the as-prepared Zn2+-triggered AIEE nanoswitch was successfully used for quantitative analysis of PPase activity in human serum with satisfactory spiked recoveries, and applied for the inhibitors screening.

Development of luminescent nanoswitch for sensing of alkaline phosphatase in human serum based onAl3+-PPi interaction and Cu NCs with AIE properties

As an important biomarker, alkaline phosphatase (ALP) is one of the most commonly assayed enzymes in clinical practice. Here a novel turn-on fluorescent nanoswitch for ALP assay was suggested. The nanoswitch was easily constructed via two high-affinity ligands between GSH and Al3+ and PPi and Al3+ based on the difference in the affinity. The primary fluorescence of as-prepared GSH capped Cu nanoclusters (NCs) turned on first upon the Al3+ addition due to the Al3+ induced aggregation induced emission (AIE) enhancement based on the high affinity of GSH and Al3+. The presence of PPi then made Al3+ desorb from the surface of GSH capped Cu NCs due to the higher affinity of PPi and Al3+. As a result, the fluorescence of the Cu NCs was quenched. ALP could hydrolyze PPi into phosphate, destroying the PPi-Al3+ complex and releasing Al3+. Thus, the Al3+ binds to GSH again and the fluorescence was restored. The nanoswitch was demonstrated to be sensitive and selective for ALP assay and was successfully used for the ALP assay in the human serum.

Antibacterial Nitrogen-doped Carbon Dots as a Reversible “Fluorescent Nanoswitch” and Fluorescent Ink

The present finding describes an efficient facile approach for the fabrication of nitrogen-doped carbon dots (N-CDs) as a “fluorescent nanoswitch”. Highly fluorescent blue-light-emitting N-CDs have been synthesized via a simpler hydrothermal method using 2,2′-(ethylenedioxy)-bis(ethylamine) and malic acid as the precursors. N-CDs showed excitation-dependent and pH-independent emission along with a quantum yield of ∼25%. The blue fluorescent emission of N-CDs has been selectively “turned off” (quenching of fluorescence (FL)) during the sensing of Cr(VI) with 0.02 μM limit of detection and further been selectively “turned on” (restoration of FL) on sensing ascorbic acid, compared with other metal cations and biomolecules tested. For testing the practical applicability of N-CDs, the switchable reversibility of the fluorescent nanoswitch has been tested for up to four cycles on the basis of FL “on–off–on”. Furthermore, the toxicological test showed the antibacterial effect of the N-CDs on the tested Gram-posi...

Near-infrared emission TMB dots as a colorimetric and fluorescent nanoswitch for the reversible recognition of iron ion and cysteine and their logic gate applications

The present work developed a facile method to fabricate a near-infrared fluorescent TMBDs colorimetric and fluorescent nanoswitch for reversible recognition (CFRR) of Fe3+ and Cys.

Polydopamine Dots-Based Fluorescent Nanoswitch Assay for Reversible Recognition of Glutamic Acid and Al3+ in Human Serum and Living Cell.

We developed a facile and feasible fluorescent nanoswitch assay for reversible recognition of glutamate (Glu) and Al3+ in human serum and living cell. The proposed nanoswitch assay is based on our recently developed method for controlled synthesis of fluorescent polydopamine dots (PDADs) at room temperature with dopamine as the sole precursor. The fluorescence of nanoswitch assay could be quickly and efficiently quenched by Glu (turn-Off), and the addition of Al3+ could recover the fluorescence of the PDADs-Glu system (turn-On). Meanwhile, the reversible recognition of Glu and Al3+ in this nanoswitch system was stable after three cycles. Additionally, the system displayed excellent performance for Glu and Al3+ determination with a low detection limit of 0.12 and 0.2 μM, respectively. Moreover, PDADs are successfully applied to determine Glu and monitor Al3+ in human serum. Noteworthy, the nanoswitch assay is transported into HepG2 cells and realized "Off" detection of Glu and "On" sensing Al3+ in the living cells. Therefore, this PDADs-based nanoswitch assay provides a strategy to develop reversible recognition biosensors for intracellular and external molecular analysis.

PH-mediated reversible fluorescence nanoswitch based on inner filter effect induced fluorescence quenching for selective and visual detection of 4-nitrophenol.

Being a common hazardous waste, 4-nitrophenol (4-NP) has caused a serious threat to humans and environment. Therefore, rapid and selective detection of 4-NP, especially using a simple and portable instrument, is highly desired for human health and environmental monitoring. Herein, we develop a novel pH-mediated reversible fluorescence nanoswitch for selectively detecting 4-NP by using water-soluble fluorescent polymer carbon dots (PCDs) as a probe. The fluorescence of PCDs can be quenched by 4-NP via inner filter effect (IFE) because its excitation spectrum well overlaps with the absorption spectrum of 4-NP under alkaline condition. However, an obvious blue shift of the absorption peak of 4-NP occurs under acidic condition, causing the fluorescence recovery of PCDs due to the disappearance of IFE. On the basis of this principle, a pH-mediated reversible fluorescence nanoswitch was constructed and a broad linear range was obtained from 0.5 to 60 μM with a detection limit of 0.26 μM for 4-NP. Furthermore, this approach was successfully applied to detect 4-NP in real water samples and a portable polyamide film-based sensor was developed for visual detection of 4-NP, which offers a promising platform for the detection of 4-NP in on-site and resource-poor settings.

Turn‐on fluorescent probe for Cd 2+ detection by gold nanoclusters/graphene oxide nanocomplex

This work reported the fabrication of bovine serum albumin stabilised gold nanoclusters (BSA-Au NCs)-graphene oxide nanocomplex (BSA-Au NCs-GO) as a `turn-on' fluorescent probe for the detection of Cd 2+ . The prepared BSA-Au NCs showed an intense red fluorescence, and the fluorescence of BSA-Au NCs was reduced significantly by graphene oxide due to its excellent quenching properties. However, in the presence of 65 μmol l -1 Cd 2+ , the fluorescence intensity recovered to 82.5% of the intensity of BSA-Au NCs, and the fluorescence intensity increased 1.3-fold relative to the BSA-Au NCs-GO nanocomplex. This proposed probe expands the application of BSA-Au NCs, which can be used as a reversible fluorescence nanoswitch for inexpensive, label free and simple detection of Cd 2+ in the aqueous samples.

Redox-Controlled Fluorescent Nanoswitch Based on Reversible Disulfide and Its Application in Butyrylcholinesterase Activity Assay.

Butyrylcholinesterase (BChE) mainly contributing to plasma cholinesterase activity is an important indicator for routinely diagnosing liver function and organophosphorus poisoning in clinical diagnosis, but its current assays are scarce and frequently suffer from some significant interference and instability. Herein, we report a redox-controlled fluorescence nanoswtich based on reversible disulfide bonds, and further develop a fluorometric assay of BChE via thiol-triggered disaggregation-induced emission. Thiol-functionalized carbon quantum dots (thiol-CQDs) with intense fluorescence is found to be responsive to hydrogen peroxide, and their redox reaction transforms thiol-CQDs to nonfluorescent thiol-CQD assembly. The thiols inverse this process by a thiol-exchange reaction to turn on the fluorescence. The fluorescence can be reversibly switched by the formation and breaking of disulfide bonds caused by external redox stimuli. The specific thiol-triggered disaggregation-induced emission enables us to assay BChE activity in a fluorescence turn-on and real-time way using butyrylthiocholine iodide as the substrate. As-established BChE assay achieves sufficient sensitivity for practical determination in human serum, and is capable of avoiding the interference from micromolar glutathione and discriminatively quantifying BChE from its sister enzyme acetylcholinesterase. The first design of reversible redox-controlled nanosiwtch based on disulfide expands the application of disulfide chemistry in sensing and clinical diagnostics, and this novel BChE assay enriches the detection methods for cholinesterase activity.

Tuning surface states to achieve the modulated fluorescence of carbon dots for probing the activity of alkaline phosphatase and immunoassay of α-fetoprotein

A convenient redox reaction was utilized to tune the surface states of carbon dots (CDs), leading to a reversibly fluorescent nanoswitch. The oxidizing treatment of CDs by KMnO4 brought about partial oxidation of hydroxyl groups to carboxyl groups, resulting in effective fluorescence quenching; reversely, the subsequent addition of ascorbic acid (AA) restored the quenched fluorescence by the reduction of the previously oxidized carboxyl groups to hydroxyl groups. Based on the redox modulated fluorescence of CDs, quantitative evaluation of alkaline phosphatase (ALP) activity in a wide range from 0.002 to 250U/L with a low detection limit of 6.0×10−4U/L was realized. In addition, this testing protocol was also expanded to an immunoassay (taking α-fetoprotein (AFP) as an example) by the cascade amplification strategy combing the hybridization chain reaction (HCR) and the ALP–based biocatalysis. A wide linear range of 1.0 fg/mL to 1.0ng/mL with a quite low detection limit of 0.2 fg/mL were obtained for the AFP assay. This study opens up a new way to modulate the fluorescence of native CDs for reversible nano-switch, which may broaden the applications of CDs in versatile bioassays.

A Novel Fluorescent Nanoswitch Based on Carbon Dots for Sensitive Detection of Hg2+ and I−

In this paper, a novel fluorescent nanoswitch based on carbon dots (CDs) was developed for the sensitive and selective determination of Hg[Formula: see text] and I[Formula: see text]. The CDs were obtained by simple hydrothermal process and had a strong fluorescence emission at 440[Formula: see text]nm. The fluorescence of the CDs can be selectively quenched by Hg[Formula: see text] ion, and then the I[Formula: see text] was added into the system, which can interact with Hg[Formula: see text] and recover fluorescence of the CDs. Under optimal conditions, the quenching fluorescence intensity on addition of Hg[Formula: see text] has obtained a satisfactory linear relationship covering the linear range of 0–50[Formula: see text][Formula: see text]M with the linear relationship ([Formula: see text]), and the limit of detection is 0.047[Formula: see text][Formula: see text]M. The additions of I[Formula: see text] could lead to the fluorescence intensity of the solution of CDs and Hg[Formula: see text] (50[Formula: see text][Formula: see text]M) recover rapidly, which is linearly related ([Formula: see text]) to the concentration of I[Formula: see text] in the range from 0 to 70[Formula: see text][Formula: see text]M, the detection limit for I[Formula: see text] was calculated to be 0.084[Formula: see text][Formula: see text]M. Moreover, the developed method to detect Hg[Formula: see text] and I[Formula: see text] was evaluated in real examples, and the fluorescence switching can sensitively and selectively detect Hg[Formula: see text] and I[Formula: see text] over some potentially interfering ions, the recoveries were up to 97.8–107.0% and 96.7–106.6%, respectively.

Fluorescent nanoswitch for monitoring specific pluripotency-related microRNAs of induced pluripotent stem cells: Development of polyethyleneimine-oligonucleotide hybridization probes

The isolation of high-grade (i.e. high-pluripotency) human induced pluripotent stem cells (hiPSCs) is a decisive factor for enhancing the purity of hiPSC populations or differentiation efficiency. A non-invasive imaging system that can monitor microRNA (miRNA) expression provides a useful tool to identify and analyze specific cell populations. However, previous studies on the monitoring/isolation of hiPSCs by miRNA expression have limited hiPSCs’ differentiation system owing to long-term incubation with miRNA imaging probe-nanocarriers. Therefore, we focused on monitoring high-grade hiPSCs without influencing the pluripotency of hiPSCs. We reduced nanoparticle transfection time, because hiPSCs are prone to spontaneous differentiation under external factors during incubation. The fluorescent nanoswitch (“ON” with target miRNA), which can be applied for either imaging or sorting specific cells by fluorescence signals, contains an miRNA imaging probe (miP) and a PEI-PEG nanoparticle (miP-P). Consequently, this nanoswitch can sense various endogenous target miRNAs within 30 min in vitro, and demonstrates strong potential for not only imaging but also sorting pluripotent hiPSCs without affecting pluripotency. Moreover, miP-P-treated hiPSCs differentiate well into endothelial cells, indicating that miP-P does not alter the pluripotency of hiPSCs. We envisage that this miRNA imaging system could be valuable for identifying and sorting high-grade hiPSCs for improved practical applications.

A reversible fluorescence nanoswitch based on dynamic covalent B–O bonds using functional carbon quantum dots and its application for α-glucosidase activity monitoring

A reversible fluorescence nanoswitch based on dynamic covalent B–O bonds that responds to the external stimulus of pH was developed, and further utilized to monitor α-glucosidase activity.

Highly specific electrochemical sensor of tumor marker using multi-nanoparticle labeling based 3D origami paper analytical device

and synthesis of a fluorescent off–on nanoprobe for MMP families (for an instance, collagenase IV, including MMP2, MMP4, and MMP9). The fabricated fluorescent nano-switch is the fluorescein isothiocyanate (FITC)-attached gold nanoparticle (GNP). The spacer inserted between FITC andGNP is a small peptide containing the core substrate sequence of MMPs and a free thiol group on the terminal cysteine. To ensure the desirable solubility, stability, and in vivo circulation of nano-switch, thiolated polyethylene glycol monomethyl ether (HS-mPEG2000) was also conjugated to the surface of GNP. The structure of the nano-switch was optimized through adjusting the molar ratio of GNP vs. p-FITC, investigating the effect on the addition of HS-mPEG2000, and evaluating fluorescence recovery efficiency of the nano-switch. Investigated using confocal laser fluorescence microscope technology, the cellular uptake result showed that with the help of GNPs, the nano-switch can bemore easily in taken byHepG2 cells (liver hepatocellular carcinoma) and lighten the greenfluorescence of FITC around GNPs inside cells. However, the green fluorescence was only found in the cell culture medium for the p-FITC group. Furthermore, tissue frozen section results demonstrated that (1) the nano-switch showed higher fluorescence intensity in tumor tissues; (2) the fluorescence recovery of the nano-switch was not only found in the margin but also in the center of tumor tissues; (3) the nano-switch exhibited lower distribution in normal tissues including heart, spleen, and lung; and (4) when comparing with p-FITC, the similar and higher accumulation of the nano-switch in liver and kidney, respectively, indicated its liver targeting and renal elimination characters.

Gold nanoparticle-based fluorescent nano-switch for the early staging diagnosis of the liver tumor

Gold nanoparticle-based fluorescent nano-switch for the early staging diagnosis of the liver tumor

Reversible Fluorescent Nanoswitch Based on Carbon Quantum Dots Nanoassembly for Real-Time Acid Phosphatase Activity Monitoring.

A reversible fluorescence nanoswitch by integrating carbon quantum dots nanoassembly and pyrophosphate ion is developed, and a reliable real-time fluorescent assay for acid phosphatase (ACP) activity is established on the basis of the fluorescence nanoswitch. Carbon quantum dots (CQDs) abundant in carboxyl groups on the surface, nickel(II) ion and pyrophosphate ion comprise the fluorescent nanoswitch, which operates in the following way: the nanoassembly consisting of CQDs and nickel ions can be triggered by pyrophosphate ion serving as an external stimulus. At the same time, the fluorescence nanoswitch switches between two fluorescence states (OFF and ON) accompanying shifts in their physical states aggregation and disaggregation. Based on the nanoswitch, the introduction of ACP leads to breakdown of pyrophosphate ions into phosphate ions and resultant fluorescence quenching due to catalytic hydrolysis of ACP toward pyrophosphate ions (PPi). Quantitative evaluation of ACP activity in a broad range from 18.2 U/L to 1300 U/L, with a detection limit of 5.5 U/L, can be achieved in this way, which endows the assay with sufficiently high sensitivity for practical detection in human serum and seminal plasma.

A reversible fluorescence nanoswitch based on carbon quantum dots nanoassembly for detection of pyrophosphate ion

A convenient and reversible nanoswitch with the assistance of cerium ions based on aggregation and disaggregation of carbon quantum dots was developed to achieve highly sensitive detection of pyrophosphate ions. Two states including aggregation state and disaggregation state corresponding to fluorescence on and off signaling can be readily switched in a reversible way. The aggregation state is resulted from large nanoassembly formed by carbon quantum dots and cerium ions due to their strong complexation affinity. The disaggregation state comes from competitive combination between cerium ion and pyrophosphate ion. The PPi ion severs as the external chemical stimulus to CQDs/Ce(III) nanoassembly, and its quantity is responsive to fluorescence intensity of the sensing system. Quantitative evaluation of PPi in a broad range from 0.3 to 29.7μM with the detection limit of 0.1μM can be realized in this way. The PPi detection in human HeLa cells was also assessed, and fluorescence switching between ON and OFF can be readily observed in response to presence and absence of PPi.

A reversible fluorescence nanoswitch based on bifunctional reduced graphene oxide: use for detection of Hg2+ and molecular logic gate operation

Herein, we demonstrate the first use of a reduced graphene oxide (rGO)-organic dye nanoswitch for the label-free, sensitive and selective detection of Hg(2+) using bifunctional rGO as an effective nanoquencher and highly selective nanosorbent. Moreover, a reversible on-off INHIBIT rGO logic gate based on a cysteine-Hg(2+) system has also been designed.