A dual recognition system with a fluorescence quenching of quantum dots (QDs) and specific recognition of molecularly imprinted polymer (MIP) for the detection of chloramphenicol (CAP) was constructed. MIP@SiO2@QDs was prepared by reverse microemulsion method with 3-aminopropyltriethoxysilane (APTS), tetraethyl orthosilicate (TEOS) and QDs being used as the functional monomer, cross-linker and signal sources, respectively. MIP can specifically recognize CAP, and the fluorescence of QDs can be quenched by CAP due to the photo-induced electron transfer reaction between CAP and QDs. Thus, a method for the trace detection of CAP based on MIP@SiO2@QDs fluorescence quenching was established. The fluorescence quenching efficiency of MIP@SiO2@QDs displayed a desirable linear response to the concentration of CAP in the range of 1.00~4.00 × 102 μmol × L−1, and the limit of detection was 0.35 μmol × L−1 (3σ, n = 9). Importantly, MIP@SiO2@QDs presented good detection selectivity owing to specific recognition for CAP, and was successfully applied to quantify CAP in lake water with the recovery ranging 102.0~104.0%, suggesting this method has the promising potential for the on-site detection of CAP in environmental waters.

构建了一种以硫化镉量子点(CdS QDs)和二氧化钛纳米颗粒(TiO2 NPs)为光敏材料的四环素光电化学适体传感器.以烧结和自组装方式将TiO2 NPs,CdS QDs修饰于ITO电极表面,制得CdS QDs/TiO2 NPs/ITO光敏电极.由于CdS QDs具有比TiO2 NPs更高的导带能级,当CdS QDs吸收420 nm的可见光被激发时,产生的光生电子(e-)将转入TiO2 NPs的导带能级,而空穴(h+)位于CdS QDs的价带能级,实现了e--h+对的分离,提高了光电转换效率.利用偶联反应将TC适体修饰于CdS QDs/TiO2 NPs/ITO光敏电极表面,适体分子所产生的空间位阻效应将抑制光电转换效率,导致光电流信号降低;而TC可与其适体发生特异性结合被电极上的适体捕获,使TC适体从光敏电极表面脱落,光电流信号因此得以恢复.结果表明:该方法在浓度为0.01～15.00μmol·L-1时呈良好的线性关系;检出限为4.2 nmol·L-1(S/N=3);加标回收率为97.6％～104.7％;且对土霉素、金霉素、氯霉素、氨苄西林等与TC相似抗生素具有较好的抗干扰能力.表明TC PEC适体传感器在检测牛奶和兽药等实际样品中的TC有较好的前景.

Kanamycin (Kana) is widely used as a veterinary medicine and its abuse causes a serious threat to human health, raising the urgent demand for detection of residual Kana in animal-derived food with high specificity and sensitivity. Here, we developed a photoelectrochemical (PEC) biosensor for rapid quantification of Kana, with lead sulfide quantum dots/titanium dioxide nanoparticles (PbS QDs/TiO2 NPs) as a photosensitive composite, a Kana-specific DNA aptamer as a functional sensor, and ruthenium(III) hexaammine (Ru(NH3)63+) as a signal booster. To prepare the PEC aptasensor, TiO2 NPs, PbS QDs, and polyethyleneimine (PEI) were respectively used to modify the indium tin oxide electrode, and then the amine-terminated aptamer probe was connected to the PEI via glutaraldehyde. Finally, Ru(NH3)63+ was attached on the surface of the aptamer to increase the photocurrent intensity. When Kana binds competitively with Ru(NH3)63+ to the aptamer immobilized on the surface of the aptasensor, Ru(NH3)63+ will be released from the aptamer, resulting in a decrease of the photocurrent signal. This PEC aptasensor exhibits a good linear relationship between the photocurrent shift and the logarithm of Kana concentration within the range of 1.0-300.0 nmol L-1, and the detection limit is 0.161 nmol L-1. Importantly, the PEC aptasensor presented good detection selectivity owing to specific interaction with Kana and was successfully implemented to quantify Kana in honey and milk, suggesting that the PEC aptasensor has the potential of rapid detection of residual Kana in animal-derived foods.

A tetraphenylporphyrin (TPP) doped PFBT polymer quantum dots (TP-Pdots) were synthesized via the reprecipitation method for photoelectrochemical (PEC) aptasensor detection of tetracycline (TC). The TP-Pdots exhibit a superior cathode photocurrent signal. TP-Pdots increase the separation of photo-generated charges, and improve photocurrent conversion efficiency, resulting in enhanced photocurrent response. The aptamer was used as a recognition element and TP-Pdots as a photoactive material to prepare a PEC aptasensor for sensitivity detection of TC. The PEC aptasensor was constructed by immobilizing TP-Pdots on ITO electrode and combining it with aptamer by EDC coupling. After the TC reacts specifically with the aptamer, causing the aptamer to fall off from the TP-Pdots /ITO electrodes surface and the photocurrent intensity restored. This PEC aptamer sensor possesses a wide linear range from 1.0 nmol.l(-1) to 1.0 x 10(4) nmol.l(-1) with the detection limit of 0.26 nmol.l(-1). Meanwhile, the PEC aptasensor was successfully used for the detection of tetracycline in honey. (C) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

A method for detecting cysteine based on fluorescenceresonance energy transfer ( FRET) between DNA quantum dots ( QDs ) and polydopamine ( PDA ) was developed. Since the fluorescence emitted by DNA QDs was absorbed by the PDA molecule, FRET occurred, resulting in fluorescence quenching of DNA QDs , and leaving the DNA QDs in a fluorescent " off " state. In the presence of cysteine , the spontaneous oxidative polymerization from dopamine ( DA ) to PDA was blocked , the fluorescence of DNA QDs was restored , and the fluorescence was " on " state. Based on this , a cysteine fluorescence sensor was developed. The sensor had good selectivity to cysteine, and there was no interference between common amino acids and small biothiol molecules. The linear equation was y = 0. 0181x -0. 0185 in linear range of 10. 0 - 100. 0 mu mol/L. The limit of detection ( LOD ) was 1. 7 mu mol/L ( S/N = 3 ) . The method was successfully applied to determination of cysteine in human urine samples , with recoveries of 98. 6% -105. 9%.

A sensitive mercury ion (Hg2+) sensor was designed by using CdS QDs/TiO2 composite material as the photoelectric conversion unit. After the coupling of two inorganic semiconductors (CdS QDs and TiO2) with different band gaps, the performance of electrode has been improved. After excited by the specific wavelength of light, the electron in CdS QDs would be motivated from the valence band to the conduction band. Then the Excited state electron would move to TiO2 due to that the valence band of TiO2 was lower than CdS QDs. The spatial separation of the e(-)-h(+) pairs in the different semiconductors could retards their recombination, and thereby the photoelectric conversion efficiency would be improved. We constructed a sensitive sensor for Hg2+ by two complementary short. stranded DNAs. One of the DNA single strands (ONS1) was rich in T bases, and Hg2+ could specifically bind to the T base to form a T-Hg2+-T structure, thus ONS1 could not be paired with complementary single stranded DNA (ONS2) labeled by gold nanoparticles (AuNPs), inhibiting the decrease of photocurrent and achieving sensitive detection of Hg2+. The Hg2+ sensor displayed a linear range from 1.0x10(-10) mol/L to 1.5x10(-7) mol/L and a detection limit of 6.0x10(-11) mol/L (S/N = 3).

Polymer dots (Pdots) represent newly developed semiconductor polymer nanoparticles and exhibit excellent characteristics as fluorescent probes. To improve the sensitivity and biocompatibility of Pdots ratiometric pH biosensors, we synthesized 3 types of water-soluble Pdots: Pdots-PF, Pdots-PP, and Pdots-PPF by different combinations of fluorescent dyes poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO), poly[(9,9-dioctyl-fluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1′,3}-thiadazole)] (PFBT), and fluorescein isothiocyanate (FITC). We found that Pdots-PPF exhibits optimal performance on pH sensing. PFO and FITC in Pdots-PPF produce pH-insensitive (λ = 439 nm) and pH-sensitive (λ = 517 nm) fluorescence respectively upon a single excitation at 380 nm wavelength, which enables Pdots-PPF ratiometric pH sensing ability. Förster resonance energy transfer (FRET) together with the use of PFBT amplify the FITC signal, which enables Pdots-PPF robust sensitivity to pH. The emission intensity ratio (I517/I439) of Pdots-PPF changes linearly as a function of pH within the range of pH 3.0 to 8.0. Pdots-PPF also possesses desirable reversibility and stability in pH measurement. More importantly, Pdots-PPF was successfully used for cell imaging in Hela cells, exhibiting effective cellular uptake and low cytotoxicity. Our study suggests the promising potential of Pdots-PPF as an in vivo biomarker.

In this study, a high fluorescence sensitivity and selectivity, molecularly imprinted nanofluorescent polymer sensor (MIP@SiO2 @QDs) was prepared using a reverse microemulsion method. 2,4,6-Trichlorophenol (2,4,6-TCP) was detected using fluorescence quenching. Tetraethyl orthosilicate (TEOS), quantum dots (QDs) and 3-aminopropyltriethoxysilane (APTS) were used as cross-linker, signal sources and functional monomer respectively. The sensor (MIP@SiO2 @QDs) and the non-imprinted polymer sensor (NIP@SiO2 @QDs) were characterized using infra-red (IR) analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The selectivity of MIP@SiO2 @QDs was examined by comparing 2,4,6-TCP with other similar functional substances including 2,4-dichlorophenol (2,4-DCP), 2,6-dichlorophenol (2,6-DCP) and 4-chlorophenol (4-CP). Results showed that MIP@SiO2 @QDs had better selectivity for 2,4,6-TCP than the other compounds. Fluorescence quenching efficiency displayed a good linear response at the 2,4,6-TCP concentration range 5-1000 μmol/L. The limit of detection (LOD) was 0.9 μmol/L (3σ, n = 9). This method was equally applicable for testing actual samples with a recovery rate of 98.0-105.8%. The sensor had advantages of simple pretreatment, good sensitivity and selectivity, and wide linear range and could be applied for the rapid detection of 2,4,6-TCP in actual samples.

Firstly, titanium dioxide nanoparticles ( TiO2 NPs) was modified to the surface of indium tin oxide ( ITO) electrode by high-temperature calcination to prepare TiO2 NPs/ITO electrode. And then sulfide quantum dots( PbS QDs) were modified to the surface of TiO2 NPs/ITO electrode by successive ionic layer adsorption and reaction( SILAR) cycle to prepare the PbS QDs/Ti02 NPs/ITO electrode. And it was used to detect glutathione( GSH). In this sensor, when PbS QDs are excited by 470 nm visible light, it will produce electrons ( e) and holes (11+). Immediately after, h+ will be captured by GSH in solution, and then GSH is oxidized into GSSH. Therefore, the recombination of electrons and holes were avoided effectively. Thus the photoelectric efficiency has been significantly improved. This sensor had satisfactory sensitivity and selectivity for GSH. what' s more, the detection range is 0. 06-1 mmol/L, and the detection limit ( LOD) is 4. 6 x 10-3 mmol/L( S/N= 3)