Nanoscale potassium sensing based on valinomycin-anchored fluorescent gold nanoclusters.

Gold nanoclusters are a smart platform for sensing potassium ions (K+). They have been synthesized using bovine serum albumin (BSA) and valinomycin (Val) to protect and cap the nanoclusters. The nanoclusters (Val-AuNCs) produced have a red emission at 616 nm under excitation with 470 nm. In the presence of K+, the valinomycin polar groups switch to the molecule's interior by complexing with K+, forming a bracelet structure, and being surrounded by the hydrophobic exterior conformation. This structure allows a proposed fluorometric method for detecting K+ by switching between the Val-AuNCs' hydrophilicity and hydrophobicity, which induces the aggregation of gold nanoclusters. As a result, significant quenching is seen in fluorescence after adding K+. The quenching in fluorescence in the presence of K+ is attributed to the aggregation mechanism. This sensing technique provides a highly precise and selective sensing method for K+ in the range 0.78 to 8 µM with LOD equal to 233 nM. The selectivity of Val-AuNCs toward K+ ions was investigated compared to other ions. Furthermore, the Val-AuNCs have novel possibilities as favorable sensor candidates for various imaging applications. Our detection technique was validated by determining K+ ions in postmortem vitreous humor samples, which yielded promising results.

Dual-emission ciprofloxacin-gold nanoclusters enable ratiometric sensing of Cu2+, Al3+, and Hg2.

An innovative triple optical sensor is presented that utilizes gold nanoclusters (GNCs) stabilized with ciprofloxacin (CIP) and bovine serum albumin (BSA). The sensor is designed to identify three critical metal ions, namely Cu2+, Al3+, and Hg2+. Under 360 nm excitation, the synthesized CIP-BSA-GNCs demonstrate dual fluorescence emission with peaks at 448 nm (blue) and 612 nm (red). The red emission is associated with the interior of the CIP-BSA-GNCs, whereas the blue emission results from the surface-bound CIP molecules. The sensitive and selective fluorescent nanosensor CIP-BSA-GNCs were employed to detect Cu2+, Al3+, and Hg2+ ions. Cu2+ effectively quenched the fluorescence intensity of the CIP-BSA-GNCs at both peaks via the internal charge transfer mechanism (ICT). Cu2+ could be detected within the concentration range 1.13 × 10-3 to 0.05 µM, with a detection limit of 0.34 nM. Al3+ increased the intensity of CIP fluorescence at 448 nm via the chelation-induced fluorescence enhancement mechanism. The fluorescence intensity of the core CIP-BSA-GNCs at 612 nm was utilized as a reference signal. Thus, the ratiometric detection of Al3+ succeeded with a limit of detection of 0.21 nM within the dynamic range 0.69 × 10-3 to 0.07 µM. Hg2+ effectively quenched the fluorescence intensity of the CIP-BSA-GNCs at 612 nm via the metallophilic interaction mechanism. The fluorescence intensity of CIP molecules at 448 nm was utilized as a reference signal. This allowed for the ratiometric detection of Hg2+ with a detection limit of 0.7 nM within the concentration range 2.3 × 10-3 to 0.1 µM.

Aminophenylboronic acid-modified nitrogen-doped graphene quantum dots and their applications in lysine sensing based on interplaying fluorescent mechanisms.

Using nitrogen-doped graphene quantum dots (N-GQDs) and 3-aminophenylboronic acid (APBA), a novel fluorescence nanosensor was developed. This nanosensor exhibits high selectivity and sensitivity for lysine detection. Its sensing mechanism involves the suppression of electron transfer from APBA to the N-GQDs unit, thereby inhibiting photoinduced electron transfer and initiating internal charge transfer. At an optimal pH of 7, the protonated α-amine and ε-amine groups of lysine interact with the amide and boronic acid moieties, respectively. This interaction results in a redshift of fluorescence, substantially enhancing the response signal. A linear response was observed within a concentration range 0.40-3.01 µM, with the detection limit being 0.005 µM. A similar linear range was also achieved for the determination of lysine in human serum. Density functional theory calculations correlating molecular orbits and geometries support UV-vis and fluorescence findings. Additionally, the nanosensor was successfully applied to detect lysine in living cells and real samples, including milk and honey. For practical application, we construct a lysine-specific sensing platform using a commercial chip (TCS34725) that collects red, blue, and green signals, thereby facilitating the convenient use of the nanosensor. Overall, this study offers new perspectives on the development and application of fluorescent nanosensors for detecting individual amino acids.

Fluorescent Switch-on Detection of Cadmium(II) Using Salicylaldehyde-Decorated Gold Nanoclusters.

In this study, salicylaldehyde (SA) conjugated gold nanoclusters were synthesized, characterized, and applied for the fluorescent turn-on sensing of Cd2+. The trypsin-stabilized fluorescent gold nanocluster (Tryp-AuNCs, λem = 680 nm) was modified with SA to form the spherical-shaped SA_Tryp-AuNCs. After modification, the red-emitting Tryp-AuNCs turned to green-emitting SA_Tryp-AuNCs because of the formation of imine linkage between the -CHO group of SA with the -NH2 group of functionalized trypsin. The modified SA_Tryp-AuNCs selectively interacted with Cd2+ and exhibited a fluorescence enhancement at 660 nm. The Cd2+ detection with SA_Tryp-AuNCs is simple and rapid with an estimated nanomolar detection limit of 98.1 nM. The practical utility of SA_Tryp-AuNCs was validated by quantifying Cd2+ in real environmental water samples.

Green synthesis of pregabalin-stabilized gold nanoclusters and their applications in sensing and drug release.

This is the first report on the simple preparation of gold nanoclusters stabilized with pregabalin (PREG) as a capping and reducing agent. PREG is an active pharmaceutical ingredient of the commercially available drug "Lyrica" used to treat different diseases like epilepsy and anxiety. PREG has never been used before in the synthesis of any nanoparticles or nanoclusters. The prepared gold nanoclusters (PREG-stabilized gold nanoclusters [PREG-AuNCs]) have blue fluorescence with excitation/emission at 365/425 nm, respectively. The reaction conditions were optimized for the synthesis of the as-prepared AuNCs. Different tools were used for the characterization of the synthesized nanoclusters in terms of size and surface properties. The PREG-AuNCs were exploited as a sensitive and selective fluorescent nanosensor for Cu2+ detection. The quenching of AuNC fluorescence intensity in the presence of Cu2+ is due to the aggregation-induced fluorescence quenching mechanism. The detection limit of Cu2+ ions was found to be 1.11 × 10-7 M. The selectivity of the PREG-AuNCs was studied and proved to be excellent. The drug entrapment efficacy and in vitro drug diffusion studies along with drug release kinetics helped to understand more about the pharmaceutical approaches of PREG-AuNCs. Moreover, we think that PREG-AuNCs open new opportunities as a promising candidate material for drug delivery systems and medical applications.

N-Doped Carbon Dots as a Fluorescent Nanosensor for Determination of Colchicine Based on Inner Filter Effect.

In this study, a novel and simple fluorescent carbon quantum dots (CQDs) based nano-sensor for colchicine determination has been prepared. The nitrogen doped CQDs probe was prepared using uric acid as a carbon/nitrogen source via a one-step pyrolysis. The sensor is based on inner filter effect (IFE) where colchicine acts as a powerful absorber that affects the excitation of the fluorescer (CQDs). This overlap results in a quantitative attenuation of the fluorescence of CQDs with increasing colchicine concentration in the range of 2-25 µM. The developed sensor has the advantages of simplicity, less time-consuming, convenience and satisfactory selectivity for colchicine determination in pharmaceutical dosage forms.

One-pot synthesis of fluorescent nitrogen and sulfur-carbon quantum dots as a sensitive nanosensor for trimetazidine determination.

Water-soluble and highly stable N,S-doped CQDs (N,S-CQDs) were synthesized using a low-cost strategy with citric acid and thiosemicarbazide in one step for use as a fluorescent nanosensor. The achieved N,S-CQDs produced strong emission at 446 nm upon excitation at 370 nm and a high quantum yield of 58.5%. The quenching effect on the prepared N,S-CQDs was utilized for determination of trimetazidine (TMZ) spectrofluorimetrically over a wide linear range 0.04-0.5 µM (0.0106-0.133 µg ml-1 ) and a low limit of detection of 0.01 µM (0.002 µg ml-1 ). Furthermore, CDs were used as a simple and rapid fluorescent probe to determine TMZ in its pharmaceutical formulations as well as in human plasma. The method was tested in compliance with International Council for Harmonisation guidelines. The results obtained were compared statistically with those given for a reported method showing no significant variation regards accuracy and precision.

Ultrafast and Energy-saving Synthesis of Nitrogen and Chlorine Co-doped Carbon Nanodots via Neutralization Heat for Selective Detection of Cr(VI) in Aqueous Phase.

In this work, it is presented for the first time that nitrogen and chlorine co-doped carbon nanodots (N,Cl-CDs) were synthesized by simply mixing glucose, concentrated hydrochloric acid (HCl), and 1,2-ethylenediamine (EDA). No external heat was employed; the neutralization reaction served as the heat source. The glucose served as the carbon source while EDA and HCl were the N and Cl dopants, respectively. The fluorescence of N,Cl-CDs was adequately quenched by hexavalent chromium Cr(VI) based on a combination of dynamic quenching and inner filter effect (IFE). Accordingly, an efficient N,Cl-CDs-based fluorescence probe was established for sensitive and selective detection of Cr(VI). The proposed fluorescence sensor provides a linear recognition range for Cr(VI) determination from 3 to 40 µM with a limit of detection (LOD) of 0.28 µM (14.6 µg/L). The proposed fluorescence method was successfully utilized to detect Cr(VI) in different water samples with satisfactory results. The spike recoveries vary from 97.01% to 103.89% with relative standard deviations (RSDs) of less than 0.82%. This work highlights the development of a simple, ultrafast, and energy-saving one-step synthetic route to fabricate N,Cl-CDs for highly selective and sensitive detection of Cr(VI) in real water samples. It is anticipated that the proposed fluorescence method could be further explored and widely used for Cr(VI) detection in the environmental industry.

Design a Friendly Nanoscale Chemical Sensor Based on Gold Nanoclusters for Detecting Thiocyanate Ions in Food Industry Applications.

The surfactant cetyltrimethylammonium bromide (CTAB) induces the aggregation of gold nanoclusters (GNCs), leading to the development of a proposed fluorometric technique for detecting thiocyanate (SCN-) ions based on an anti-aggregation mechanism. This approach is straightforward to execute, highly sensitive, and selective. A significant quenching effect occurs in fluorescence upon using the aggregation agent CTAB in GNCs synthesis, resulting in a transition from intense red fluorescence to dim red. The decrease in fluorescence intensity of GNCs in the presence of CTAB is caused by the mechanism of fluorescence quenching mediated by aggregation. As the levels of SCN- rise, the fluorescence of CTAB-GNCs increases; this may be detected using spectrofluorometry or by visually inspecting under UV irradiation. The recovery of red fluorescence of CTAB-GNCs in the presence of SCN- enables the precise and discerning identification of SCN- within the concentration range of 2.86-140 nM. The minimum detectable concentration of the SCN- ions was 1 nM. The selectivity of CTAB-GNCs towards SCN- ions was investigated compared to other ions, and it was demonstrated that CTAB-GNCs exhibit exceptional selectivity. Furthermore, we believe that CTAB-GNCs have novel possibilities as favorable sensor candidates for various industrial applications. Our detection technique was validated by analyzing SCN- ions in milk samples, which yielded promising results.

Dual factor coactivatable fluorescent nanosensor with boosted cytoplasmic biomarker accessibility toward selective tumor imaging.

Fluorescent nanosensor-based tumor imaging holds great promise in cancer diagnosis and treatment assistance, yet the signal contrast is heavily hampered by the unspecific/unwanted activation at microscopic regions with a highly restricted local abundance of biomarkers. Herein, we developed an activation boosting strategy by the integration and manipulation of dual-factor coactivation of sensing and lysosome escape facilitated the rise of cytosolic biomarker accessibility. By employing hybrid DNA probes on gold nanoquenchers, ATP sensing initiated conformation switch of the corresponding aptamer units triggered the exposure of a hidden toehold in a loop structure. Sequentially, miRNA-21 sensing was triggered by toehold-mediated strand displacement and detachment of the binding complexes. The application of lysosomotropic agent chloroquine at optimized time interval facilitated the release of nanosensors into the cytosol and a ∼10.5-fold increment of intracellular fluorescence in vitro, while coactivation improved the cancer-to-normal cell signal ratio by ∼5.9 times. The synergy effects led to a high tumor-to-normal tissue ratio value of ∼7.9 in the in vivo imaging results. This strategy establishes a new paradigm of fluorescent nanosensors for selective and specific tumor imaging.

Simultaneous Visualization of MiRNA-221 and Caspase-3 in Cancer Cells for Investigating the Feasibility of MiRNA-Targeted Therapy with a Dual-Color Fluorescent Nanosensor.

MiRNA-targeted therapy holds great promise for precision cancer therapy. It is important to investigate the effect of changes in miRNA expression on apoptosis in order to evaluate miRNA-targeted therapy and achieve personalized therapy. In this study, we designed a dual-color fluorescent nanosensor consisting of grapheme oxide modified with a molecular beacon and peptide. The nanosensor can simultaneously detect and image miRNA-221 and apoptotic protein caspase-3 in living cells. Intracellular experiments showed that the nanosensor could be successfully applied for in situ monitoring of the effect of miRNA-221 expression changes on apoptosis by dual-color imaging. The current strategy could provide new avenues for investigating the feasibility of miRNA-targeted therapy, screening new anti-cancer drugs targeting miRNA and developing personalized treatment plans.

Dual Optical Nanosensor Based on Ormosil Nanoparticles for Monitoring O2 and pH.

Monitoring O2 and pH has excellent potential in different sensing applications, especially in biological and clinical applications. This report presents a protocol for synthesizing an optical dual nanosensor for those two parameters. The organically modified silica (ormosil) nanoparticles were prepared based on phenytrimethoxysilane in an aqueous solution using an acid-base one-pot strategy. Ormosil was selected as a lipophilic matrix for loading fluorescent O2-sensitive dye platinum(II)-tetrakis-(pentafluorophenyl) porphyrin (Pt-TPFPP), which was quenched in the presence of O2 gas and exhibited a considerable detection proficiency within a percentage range of (0-100%) O2. Commercially available drug ingredient salicylamide was labeled on the surface of the nanoparticles using a coupling agent (3-glycidoxypropyl) trimethoxysilane (GPTMS). For measuring pH, salicylamide acted for the first time as a pH-sensitive probe based on a turn-on process with increasing pH. The nanosensor displayed a significant pH detection efficiency in the range of (pH = 6-10). Salicylamide turn-on fluorescence was attributed to the excited state intramolecular transfer (ESIPT) process followed by the inter charge transfer (ICT). The presented dual nanosensor opens new opportunities as a promising candidate material for industrial systems and medical applications.

A Portable Smartphone Platform Using a Ratiometric Fluorescent Paper Strip for Visual Quantitative Sensing.

Instrument-free, portable, and direct read-out mini-devices have wider application prospects in various fields, especially for real-time/on-site sensing. Herein, combined with a paper strip, a smartphone sensing platform integrated with a UV lamp and dark cavity by 3D-printing technology has been developed for the rapid, sensitive, instrument-free, and visual quantitative analysis in real-time/on-site conditions. The platform proved the feasibility for visual quantitative detection of pesticide via a fluorescence "on-off-on" response with a single dual-emissive ratiometric paper strip. Red-emitting CdTe quantum dots (rQDs) were embedded into the silica nanoparticles (SiO2 NPs) as an internal reference, while blue-emitting carbon dots (bCDs) as a signal report unit were covalently linked to the outer surface of SiO2 NPs. The blue fluorescence could be quenched by gold nanoparticles (Au NPs) and then recovered with pesticide. The red (R), green (G), and blue (B) channel values of the generated images were determined by a color recognizer application (APP) installed in the smartphone, and the R/B values could be used for pesticide quantification with a sensitive detection limit (LOD) of 59 nM. The smartphone sensing platform based on 3D printing might provide a general strategy for visual quantitative detection in a variety of fields including environments, diagnosis, and safety monitoring.

Direct Monitoring of Cancer-Associated mRNAs in Living Cells to Evaluate the Therapeutic RNAi Efficiency Using Fluorescent Nanosensor.

Cancer-associated mRNA (mRNA) is an important biomarker for early diagnosis, prognosis, and prediction of treatment responses. Despite recent developments in fluorescence live cell imaging, reliable detection and quantification of mRNA in living cells still remain challenging due to a complicated intracellular environment. Herein, we present a fluorescent nanosensor for live-cell monitoring of cancer-related mRNAs involved in the canonical Wnt/ß-catenin signaling pathway. The nanosensor enables rapid and accurate assessment of gene downregulation efficiency in a dose- and time-dependent manner by measuring quantitative fluorescence signal corresponding to ß-catenin or its target mRNA levels in living cells. It is expected that the fluorescent nanosensor will be applicable to high-throughput screening for the efficient drug discovery and insightful understanding of the molecular mechanisms of potential drug candidate for cancer treatment.

On-off-on fluorescent carbon dots from waste tea: Their properties, antioxidant and selective detection of CrO42-, Fe3+, ascorbic acid and L-cysteine in real samples.

In this work, we reported an economical plant-based hydrothermal method for one-pot green synthesis of water-soluble carbon dots (Tea-CDs) by using waste tea extract as a carbon source. The synthesized Tea-CDs were characterized by UV-visible, fluorescence, FT-IR, TEM, XPS and XRD. The Tea-CDs were found to remove hydroxyl and superoxide anion radical in vitro. In addition, the Tea-CDs exhibited bright blue fluorescence under UV-light (λex = 365 nm), and the fluorescence could be effectively quenched by CrO42- and Fe3+ ions. Meanwhile, the fluorescence of Tea-CDs-CrO42- and Tea-CDs-Fe3+ systems could be again easily recovered by ascorbic acid (AA) and L-cysteine (L-Cys). As an on-off-on fluorescent nano-sensor of the Tea-CDs, the sensitive detection of CrO42-, Fe3+, AA and L-Cys were all performed, showing that the good linear relationships between fluorescence intensity of Tea-CDs and concentration of all testing samples. Finally, the sensors successfully detected CrO42-, Fe3+, AA and L-Cys in commercially available real samples with satisfactory recovery ranges. The prepared sensors offer distinct advantages including low cost, simple handling, good sensitivity and high selectivity.

An ultrasensitive fluorescent nanosensor for trypsin based on upconversion nanoparticles.

Trypsin and its inhibitors are relevant to many physiological processes and diseases. In this study, a nanosensor capable of detecting trypsin and its inhibitors was designed based on the fluorescence resonance energy transfer (FRET) between upconversion nanoparticle (UCNP) and gold nanoparticle (AuNP). UCNP and AuNP were linked by a trypsin-sensitive peptide DDDDARC, forming the non-fluorescent UCNP-peptide-AuNP nanosensor. In the presence of trypsin, the peptide was cleaved and the quenched fluorescence was restored; in the presence of trypsin inhibitors, the recovery of the fluorescence was decreased. The nanosensor showed a superb sensitivity and selectivity for trypsin and its inhibitors, with a detection limit of 4.15ngmL-1 for trypsin. UCNP-peptide-AuNP could eliminate the interference of background fluorescence and avoid the light toxicity, and potentially be used to diagnose trypsin-related diseases or screen trypsin inhibitors.

Multiparametric Magneto-fluorescent Nanosensors for the Ultrasensitive Detection of Escherichia coli O157:H7.

Enterohemorrhagic Escherichia coli O157:H7 presents a serious threat to human health and sanitation and is a leading cause in many food- and waterborne ailments. While conventional bacterial detection methods such as PCR, fluorescent immunoassays and ELISA exhibit high sensitivity and specificity, they are relatively laborious and require sophisticated instruments. In addition, these methods often demand extensive sample preparation and have lengthy readout times. We propose a simpler and more sensitive diagnostic technique featuring multiparametric magneto-fluorescent nanosensors (MFnS). Through a combination of magnetic relaxation and fluorescence measurements, our nanosensors are able to detect bacterial contamination with concentrations as little as 1 colony-forming unit (CFU). The magnetic relaxation property of our MFnS allow for sensitive screening at low target CFU, which is complemented by fluorescence measurements of higher CFU samples. Together, these qualities allow for the detection and quantification of broad-spectrum contaminations in samples ranging from aquatic reservoirs to commercially produced food.

Reusable sensor based on functionalized carbon dots for the detection of silver nanoparticles in cosmetics via inner filter effect.

We report a low cost selective analytical method based on inner filter effect (IFE) for citrate-silver nanoparticle (cit-AgNP) detection, in which fluorescent amine-derivatized carbon dots (a-CDs) act as the donor and aggregated cit-AgNPs as the energy receptor. Carbon dots (CDs) were chemically modified with ethylenediamine (EDA) moieties via amidic linkage displaying an emission band at 440nm. The presence of cit-AgNPs produces a remarkably quenching of a-CD fluorescence via IFE, since the free amine groups at CD surface induce the aggregation of cit-AgNPs accompany by a red-shifting of their characteristic plasmon absorption wavelength, which resulted in "turn-on" of the IFE-decreased in CD fluorescence. The proposed method, which involves the use of chelating agents for removal of metal ions interferences, exhibits a good linear correlation for detection of cit-AgNPs from 1.23×10(-5) to 6.19×10(-5) mol L(-1), with limits of detection (LOD) and quantification (LOQ) of 5.17×10(-6) and 1.72×10(-5) mol L(-1,) respectively. This method demonstrates to be efficient and selective for the determination of cit-AgNPs in complex matrices such as cosmetic creams and reveals many advantages such as low cost, reusability, high sensitivity and non time-consuming compared with other traditional methods.