Recent advances and applications in QDs-based sensors

As a unique nanomaterial, quantum dots (QDs) are not only applied in fluorescent labeling and biological imaging, but are also utilized in novel sensing systems. Because QDs have attractive optoelectronic characteristics, QD-based sensors present high sensitivity in detecting specific analytes in the chemical and biochemical fields. In this review, we describe the basic principles and different conjugation strategies in QD-based sensors. An overview of recent advances and various models of QD-sensing systems is also provided. Furthermore, perspectives for sensors based on QDs are discussed.     

Shape-controlled synthesis of polyhedral CdS flowerlike architectures and their optical properties

Fabrication of polyhedral CdS flower-like architectures have been achieved on a large scale through a mixed solvothermal method. The obtained CdS are characterized by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy, and the results indicate that the CdS flower-like architectures with diameters of 1.5–2.0 µm are hexagonal wurtzite phase and are assembled by some pyramids with the bottom side length of about 440 nm, which have some crystallographic faces. A series of relevant experiments through altering experimental parameters, indicate that the temperature, starting materials and solvent play key roles for the shape evolution of CdS flower-like architectures. The studies of optical properties for polyhedral CdS flower-like architectures indicate that the UV-vis spectroscopy shows a blue-shift absorption peak at 500 nm compared to that of bulk CdS, the photoluminescence spectroscopy shows an emission peak at 640 nm and another strong emission peak at 695 nm, which are believed to be attributed to excitonic emission and deep levels.      

Visual and fluorescent detection of acetamiprid based on the inner filter effect of gold nanoparticles on ratiometric fluorescence quantum dots

In this work, we develop a simple and rapid sensing method for the visual and fluorescent detection of acetamiprid (AC) based on the inner-filter effect (IFE) of gold nanoparticles (AuNPs) on ratiometric fluorescent quantum dots (RF-QDs). The RF-QDs based dual-emission nanosensor was fabricated by assembling green emissive QDs (QDs_539 nm, λ_em = 539 nm) on the surface of red emissive QDs (QDs_661 nm, λ_em = 661 nm)-doped silica microspheres. The photoluminescence (PL) intensity of RF-QDs could be quenched by AuNPs based on IFE. Acetamiprid can adsorb on the surface of AuNPs due to its cyano group that has good affinity with gold, which could induce the aggregation of AuNPs accompanying color change from red to blue. Thus, the IFE of AuNPs on RF-QDs was weakened and the PL intensity of RF-QDs was recovered accordingly. Under the optimized conditions, the PL intensity of the RF-QDs/AuNPs system was proportional to the concentration of AC in the range of 0.025–5.0 μg mL⁻¹, with a detection limit of 16.8 μg L⁻¹. The established method had been used for AC detection in environmental and agricultural samples with satisfactory results.     

A convenient and label-free fluorescence “turn off–on” nanosensor with high sensitivity and selectivity for acid phosphatase

In this study, we reported a convenient label-free fluorescence nanosensor for rapid detection of acid phosphatase on the basis of aggregation-caused quenching (ACQ) and enzymolysis approach. The selectivity nanosensor was based on the fluorescence “turn off–on” mode, which possessed high sensitivity features. The original strong fluorescence intensity of CuInS₂ QDs was quenched by sodium hexametaphosphate (NaPO₃)₆. The high efficiency of the quenching was caused by the non-covalent binding of positively charged CuInS₂ QDs to the negatively charged (NaPO₃)₆ through electrostatic interactions, aggregating to form a CuInS₂ QDs/(NaPO₃)₆ complex. Adding acid phosphatase caused intense fluorescence of CuInS₂ QDs/(NaPO₃)₆ to be recovered, and this was because of enzymolysis. (NaPO₃)₆ was hydrolyzed into small fragments and the high negative charge density decreased, which would weaken the strong electrostatic interactions. As a result, the quenched fluorescence “turned on”. Under the optimum conditions, there was a good linear relationship between I/I₀ (I and I₀ were the fluorescence intensity of CuInS₂ QDs/(NaPO₃)₆ system in the presence and absence of acid phosphatase, respectively) and acid phosphatase concentration in the range of 75–1500 nU mL⁻¹ with the detection limit of 9.02 nU mL⁻¹. The proposed nanosensor had been utilized to detect and accurately quantify acid phosphatase in human serum samples with satisfactory results.     

A near-infrared fluorescent bioassay for thrombin using aptamer-modified CuInS2 quantum dots

We describe a near-infrared (NIR) fluorescent thrombin assay using a thrombin-binding aptamer (TBA) and Zn(II)-activated CuInS₂ quantum dots (Q-dots). The fluorescence of Zn(II)-activated Q-dots is quenched by the TBA via photoinduced electron transfer, but if thrombin is added, it will bind to TBA to form G-quadruplexes and the Q-dots are released. As a result, the fluorescence intensity of the system is restored. This effect was exploited to design an assay for thrombin whose calibration plot, under optimum conditions, is linear in the 0.034 to 102 nmol L⁻¹ concentration range, with a 12 pmol L⁻¹ detection limit. The method is fairly simple, fast, and due to its picomolar detection limits holds great potential in the diagnosis of diseases associated with coagulation abnormalities and certain kinds of cancer.

We developed a simple near-infrared fluorescence assay using thrombin binding aptamer (TBA) and Zn(II)-activated CuInS₂ quantum dots for the highly selective and sensitive detection of thrombin.

     

大直径钪酸盐阴极发射特性

 为获得kA级热发射电子束,研制了直径为100 mm钪酸盐热阴极组件,并建立了适应大面积热阴极实验环境的2 MV 注入器试验平台。实验在二极管真空3.7×10^-5 Pa、二极管电压1.95 MV、脉宽120 ns（FWHM）、阴极温度1 120 ℃时,获得最大收集电流1 038 A,发射电流密度约13 A/cm²。实验结果表明,工作状态下阴极发射能力与激活温度、系统真空度关系密切。     

A novel optical nanoprobe for trypsin detection and inhibitor screening based on Mn-doped ZnSe quantum dots

In this paper, a novel optical nanoprobe (Mn:ZnSe d-dots-Arg₆) for trypsin detection and its inhibitor screening has been constructed successfully based on the fluorescence quenching and recovery of Mn:ZnSe d-dots. Mn:ZnSe d-dots would aggregate in the presence of positively charged Arg₆ (six arginine residues) due to electrostatic interactions that result in the fluorescence quenching. Arg₆ can be hydrolyzed into small fragments in the presence of trypsin, and accordingly, the aggregation of Mn:ZnSe d-dots can be prohibited, which lead to the fluorescence recovery. Experimental results show that the recovery in fluorescence intensity is linearly proportional to the concentration of trypsin within the range of 0.1–12.0 μg mL⁻¹ with a detection limit of 40 ng mL⁻¹ under the optimized experimental conditions. We also prove the feasibility of fluorescence recovery of Mn:ZnSe d-dots for trypsin detection through the resonance light scattering (RLS) technique. Additionally, the optical nanoprobe can be employed for screening the inhibitors of trypsin. The optical nanoprobe was successfully applied for the determination of trypsin in human serum and urine samples with good accuracy and satisfactory recovery.     

Machine learning designs non-hemolytic antimicrobial peptides

Machine learning (ML) consists of the recognition of patterns from training data and offers the opportunity to exploit large structure–activity databases for drug design. In the area of peptide drugs, ML is mostly being tested to design antimicrobial peptides (AMPs), a class of biomolecules potentially useful to fight multidrug-resistant bacteria. ML models have successfully identified membrane disruptive amphiphilic AMPs, however mostly without addressing the associated toxicity to human red blood cells. Here we trained recurrent neural networks (RNN) with data from DBAASP (Database of Antimicrobial Activity and Structure of Peptides) to design short non-hemolytic AMPs. Synthesis and testing of 28 generated peptides, each at least 5 mutations away from training data, allowed us to identify eight new non-hemolytic AMPs against Pseudomonas aeruginosa, Acinetobacter baumannii, and methicillin-resistant Staphylococcus aureus (MRSA). These results show that machine learning (ML) can be used to design new non-hemolytic AMPs.

Machine learning models trained with experimental data for antimicrobial activity and hemolysis are shown to produce new non-hemolytic antimicrobial peptides active against multidrug-resistant bacteria.     

Detection of ascorbic acid and folic acid based on water-soluble CuInS(2) quantum dots

In this paper, water-soluble CuInS(2) ternary quantum dots (QDs) modified by mercaptopropionic acid (MPA) were directly synthesized by hydrothermal method. Ascorbic acid (AA) can induce the fluorescence enhancement of MPA-capped CuInS(2) QDs and can be used for the detection of AA. Under the optimized conditions, the relationship between the fluorescence intensity of the CuInS(2) QDs and AA concentration was linear in the range of 0.25-200 μmol?L(-1). Most relevant molecules and physiological ions had no effect on the detection of AA. The fluorescence intensity of CuInS(2) QDs enhanced by a certain amount of AA could be reduced in the presence of folic acid (FA) and thus can be used for the detection of FA with the linear range of 0.2-100 μmol?L(-1). Compared with previous reports, the established approach utilized a simple, sensitive, and selective strategy to develop the QDs probe based on fluorescence enhancing and quenching phenomena without complicated immobilization.     

天鹅绒与碳纳米管阴极强流脉冲发射特性

在2 MeV直线感应加速器注入器平台上开展了天鹅绒阴极与碳纳米管阴极的强流脉冲发射特性综合实验。研究结果表明:天鹅绒阴极与碳纳米管阴极均具有强流脉冲发射性能,在1.61 MV的二极管电压下,天鹅绒阴极与碳纳米管的发射电流密度分别为84,108 A/cm2;启动时间分别为21,40 ns;放气量分别为0.29,0.91 PaL;放出气体分子数目与发射电子数目之比分别为64,225;两种冷阴极强流脉冲发射时的放气质谱相似。