L-Histidine-DNA interaction: a strategy for the improvement of the fluorescence signal of poly(adenine) DNA-templated gold nanoclusters

An electrochemiluminescence microsensor based on DNA-silver nanoclusters amplification for detecting cellular adenosine triphosphate

Adenosine triphosphate (ATP), as the primary energy source, plays vital roles in many cellular events. Developing an efficient assay is crucial to rapidly evaluate the level of cellular ATP. A portable and integrated electrochemiluminescence (ECL) microsensor array based on a closed bipolar electrode (BPE) was presented. In the BPE unit, the ECL chemicals and oxidation/reduction were separated from the sensing chamber. The ATP aptamer was assembled with single-stranded DNA (ssDNA) in the sensing chamber. ATP capture made the aptamer disassemble from the ssDNA and facilitated DNA-templated silver nanocluster (Ag NC) generation by the target-rolling circle amplification (RCA) reaction. The guanine-rich padlock sequence produced tandem periodic cytosine-rich sequences by the RCA, inducing Ag NC generation in the cytosine-rich region of the produced DNA strands through Ag+ reduction. The in situ Ag NC generation enhanced the circuit conductivity of the BPE and promoted the ECL reaction of [Ru(bpy)2dppz]2+/tripropylamine in the anodic reservoir. On this ECL microsensor, a good linear relationship of ATP was achieved ranging from 30 to 1000 nM. The ATP content in HepG2 cells was selectively and sensitively determined without complex pretreatment. The ATP amount of 25 cells could be successfully detected when a sub-microliter sample was loaded.

Antimicrobial Agent Functional Gold Nanocluster-Mediated Multichannel Sensor Array for Bacteria Sensing

Urinary tract infections (UTIs) have greatly affected human health in recent years. Accurate and rapid diagnosis of UTIs can enable a more effective treatment. Herein, we developed a multichannel sensor array for efficient identification of bacteria based on three antimicrobial agents (vancomycin, lysozyme, and bacitracin) functional gold nanoclusters (AuNCs). In this sensor, the fluorescence intensity of the three AuNCs was quenched to varying degrees by the bacterial species, providing a unique fingerprint for different bacteria. With this sensing platform, seven pathogenic bacteria, different concentrations of the same bacteria, and even bacterial mixtures were successfully differentiated. Furthermore, UTIs can be accurately identified with our sensors in ∼30 min with 100% classification accuracy. The proposed sensing systems offer a rapid, high-throughput, and reliable sensing platform for the diagnosis of UTIs.

A ThT Derivative as Zn2+ Sensor Based on DNA G-quadruplex

In this report, we developed a sensing strategy based on ThT-E (a ThT derivative) and DNA G-quadruplex for the label-free detection of Zn2+. In the absence of Zn2+, there was a fluorescence enhancement of ThT-E by interaction with human telomere sequence. On the addition of Zn2+, Zn2+ induced a more compact antiparallel G-quadruplex to release ThT-E, resulting in fluorescence quenching. The detection limit was 0.6996 μM, and the fluorescence intensity showed a good linear relationship with the concentration of Zn2+ in the range of 0-10 μM. This sensing strategy which only needs to mix two kinds of materials has the characteristics of label-feel, simple operation, short response time, economical and efficient.

A Sensitive Fluorescence Sensor for Tetracycline Determination Based on Adenine Thymine-Rich Single-Stranded DNA-Templated Copper Nanoclusters

A sensitive fluorescent sensor has been developed for the determination of tetracycline (TC) using adenine thymine (AT)-rich single-stranded DNA (ssDNA) templated copper nanoclusters (CuNCs) as a fluorescent probe. Fluorescent ssDNA-CuNCs were synthesized by employing AT-rich ssDNA as templates and ascorbic acid as reducing agents through a facile one-step method. The as-prepared ssDNA-CuNCs exhibited strong fluorescence with a large Stokes shift (240 nm) and stable fluorescence emission. In the presence of TC, the fluorescent intensity of ssDNA-CuNCs was obviously decreased through the inner filter effect, due to the spectral overlapping between ssDNA-CuNCs and TC. Under the optimal conditions, the strategy exhibited sensitive detection of TC with a linear range from 2 nM to 30 μM and with a limit of detection of 0.5 nM. Furthermore, the sensor was successfully applied for the detection of TC in milk samples. Therefore, it provided a simple, rapid, and label-free fluorescent method for TC detection.

A microgel of CdSe quantum dots for fluorescent bisphenol A detection

A fluorescent microgel for BPA detection has been successfully prepared by cross-linking linear poly(styrene-co-glycidyl methacrylate) (poly (STY-co-GMA)) with L-cysteine-capped CdSe quantum dots (Lcys-caped CdSe QDs). The microgel contained specific binding sites created by the covalent grafting of the copolymer onto the QDs via the GMA units, allowing for selective trapping of BPA molecules through π-π and hydrogen bond interactions with phenyl, carboxylic, and amine groups. After binding, electron transfer from the QDs to the analyte quenched the fluorescence at a wavelength of 547 nm when excited at 400 nm. The rational compositional and structural design allows the microgel to accurately detect BPA concentrations over a wide dynamic range of 1.0×10^-1 to 1.0×10⁵ μg/L with a low detection limit (7.0×10^-2 to 8.0×10^-2 μg/L) in deionized, drinking, and tap waters within just 2.0 min. On top of that, the sensitivity for BPA detection was 2.0-4.6 times higher than that of the other 3 structural analogues, even molecular imprinting was not involved. The influence of the STY/GMA compositions in the copolymers and environmental conditions, including pH and ionic strength, on the sensing performance was determined. Moreover, the sensing mechanism and the selectivity with respect to the molecular features were elucidated.

Determination of trypsin using protamine mediated fluorescent enhancement of DNA templated Au nanoclusters

A fluorescent method is described for trypsin determination through the strong electrostatic interactions between cationic polyelectrolytes and single-stranded DNA (ssDNA) templated Au nanoclusters (AuNCs). The ssDNA-AuNCs display improved fluorescence emission with excitation/emission maxima at 280/475 nm after being incorporated with poly(diallyldimethylammonium chloride) (PDDA). Fluorescent enhancement is mainly attributed to the electrostatic interactions occurring  between PDDA and ssDNA templates. This can make the conformation of the ssDNA templates to change. Thus, it offers a better microenvironment for stabilizing and protecting ssDNA-AuNCs, and results in fluorescence emission enhancement. By using protamine as a model, the method is employed for the determination of trypsin. The assay enables trypsin to be determined with good sensitivity and a linear response ranging from 5 ng⋅mL^-1 to 60 ng⋅mL^-1 with a 1.5 ng⋅mL^-1 limit of detection. It is also extended to determine  the trypsin contents in human's serum samples with recoveries between 98.7% and 103.5% with relative standard deviations (RSDs) between 3.5% and 4.8%. A novel fluorescent strategy has been developed for of trypsin determination by using protamine mediated fluorescent enhancement of DNA templated Au nanoclusters.

Glucose and pH responsive fluorescence detection system based on simple synthesis of silicon-coated perovskite quantum dots

Perovskite quantum dots (PQDs) are extremely unstable in ambient air due to their inherent structural instability, which limits the wide application of PQDs. In this work, silicon-coated CsPbBr₃ PQDs (CsPbBr₃@SiO₂) was synthesized via a simple method. The SiO₂ coating effectively isolated PQDs from water and oxygen in the environment, which were the main elements that destroyed the structure stability of PQDs. The synthesized CsPbBr₃@SiO₂ can be stored in water for more than 2 months and posessed wonderful dispersibility in aqueous solution. The fluorescence intensity remained unchanged within 7 days and only decreased by 11.9 % within 2 months. We found that CsPbBr₃@SiO₂ was extremely sensitive to environmental pH, and the fluorescence intensity decreased with the reduction of pH. In addition, an excellent linear relationship with pH value in the range of 1.0 ∼ 5.0 was achieved. As we all known that glucose can be catalyzed by glucose oxidase to produce gluconic acid and hydrogen peroxide, in which a good deal of protons were produced and the pH was gradually lowered. Since CsPbBr₃@SiO₂ was stable to water and oxygen, and sensitive to ambient pH, we applied CsPbBr₃@SiO₂ to the detection of glucose. CsPbBr₃@SiO₂ showed fantastic selectivity and sensitivity to glucose, and the detection limit can even reach 18.5 μM. Furthermore, CsPbBr₃@SiO₂ was successfully applied to the detection of glucose in the human serum with satisfactory performance.

Glutathione-stabilized copper nanoclusters mediated-inner filter effect for sensitive and selective determination of p-nitrophenol and alkaline phosphatase activity

A simple and highly selective fluorescence biosensor has been exploited for p-nitrophenol (p-NP) and alkaline phosphatase (ALP) activity detection based on the glutathione-stabilized copper nanoclusters (GSH-CuNCs) mediated-inner filter effect (IFE). The GSH-CuNCs were prepared by employing GSH as stabilizer and ascorbic acid (AA) as reductant. The obtained GSH-CuNCs exhibited a strong blue fluorescence emission at 420 nm with an excitation wavelength of 365 nm, which overlapped largely with the absorption spectra of p-nitrophenol (p-NP). Therefore, the luminescence of GSH-CuNCs could be quenched by p-NP through inner filter effect. In addition, ALP catalyzed the substrate p-nitrophenyl phosphate (p-NPP) to form p-nitrophenol (p-NP), which also leading to the fluorescence quenching of GSH-CuNCs. The fluorescent strategy was realized for the sensitive determination of p-NP and ALP activity with the promising limit of detection of 20 nM (for p-NP) and 0.003 mU⋅mL^-1 (for ALP). Furthermore, the method could be applied to detect the p-NP content in river water samples and ALP activity in human serum samples.