In this paper, a facilely prepared electrochemiluminescence (ECL) biosensor was developed for Escherichia coli O157:H7 quantitative detection based on a polydopamine (PDA) surface imprinted polymer (SIP) and nitrogen-doped graphene quantum dots (N-GQDs). N-GQDs with a high quantum yield of 43.2% were synthesized. The uniform PDA SIP film for E. coli O157:H7 was established successfully with a facile route. The dopamine and target bacteria were electropolymerized directly on the electrode. After removal of the E. coli O157:H7 template, the established PDA SIP can selectively recognize E. coli O157:H7. Accordingly, E. coli O157:H7 polyclonal antibody (pAb) was labeled with N-GQDs. The bioconjugation of SIP–E. coli O157:H7/pAb-N-GQDs can generate intensive ECL irradiation with K2S2O8. As a result, E. coli O157:H7 was detected with the ECL sensing system. Under optimal conditions, the linear relationships between the ECL intensity and E. coli O157:H7 concentration were obtained from 101 colony-forming units (CFU) mL–1 to 107 CFU mL–1 with a limit of detection of 8 CFU mL–1. The biosensor based on this SIP film was applied in water sample detection successfully. The N-GQD-based ECL analytical method for E. coli O157:H7 was reported for the first time. The sensing system had high selectivity to the target analyte, provided new opportunities for use, and increased the rate of disease diagnosis and treatment and the prevention of pathogens.Keywords: dopamine; E. coli O157:H7; electrochemiluminescence; electropolymerization; nitrogen-doped graphene quantum dot; surface imprinted polymer;

A modulated photoluminescence nanosensor was developed for the quantitative detection of formaldehyde with nitrogen-doped graphene quantum dots and melamine. The sensing system was based on the different activated effects of melamine and hydrogen peroxide on the photoluminescence intensity of nitrogen-doped graphene quantum dots. Under the optimal conditions, the modulated photoluminescence sensing system can be used to detect formaldehyde with a good linear relationship between the nitrogen-doped graphene quantum dots photoluminescence difference and the concentration of formaldehyde. The novel sensing system provided new directions for the detection of formaldehyde with high selectivity and quick response.

In this paper, a novel electrochemiluminescence (ECL) sensor for lysophosphatidic acid (LPA) detection was developed. LPA consists of a phosphate “head” group, a “linker” region illustrated by glycerol, and a fatty acyl chain as a lipophilic “tail”. The water-soluble quaternary CuInZnS quantum dots (QDs) were modified with agmatine (AGM) molecules as an ECL luminophore. On the one hand, the guanidine groups on the QDs can capture the hydrophilic head of LPA with high selectivity. On the other hand, the electrochemically reduced graphene nanosheets (GNs) modified on the glassy carbon electrode (GCE) surface can bind the LPA lipophilic tail. As a result, the LPA-AGM-CuInZnS QDs were captured on the GNs/GCE. The ECL intensity of the system was enhanced with the increased concentration of LPA. As far as we know, it was the first report about LPA detection based on the ECL nanosensing system. The linear relationship range of LPA sensing is from 2 to 75 μmol L−1. The practicability of this ECL sensing platform had shown satisfactory results in human serum samples.

In this work, we developed an aqueous synthetic strategy for a new kind of hydrophilic multicolor Cu-Zn-In-S quantum dots (CIZS QDs). The CIZS QDs possessed not only the good water solubility but also additional superiority such as low toxicity and good chemical stability. The synthesis conditions of high quality CIZS QDs with tunable fluorescence color, including precursor ratio, reaction time, and temperature, have been studied deeply. As a result, the photoluminescence (PL) emission peaks of the CIZS QDs can be controlled from 450 nm to 664 nm based on the different ratio of In: Zn. To the best of our knowledge, it is the first report about the synthesis of multicolor hydrophilic CIZS QDs. The fast-speed growth and good photo stability of multicolor CIZS QDs showed that this proposed facile aqueous synthetic route had largely improved chemical optical performance of CIZS QDs, which had potential in chemo/biosensing and bioimaging.

Dopamine (DA) was sensitively detected using a label-free fluorescence method using nitrogen-doped graphene quantum dots (N-GQDs) as effective probes. The detection of DA was also performed on the N-GQD immersed filter paper. The fluorescence intensity of the N-GQDs was effectively quenched upon addition of DA. There was a good linear relationship between the fluorescence intensity of the N-GQDs and the DA concentration in the range of 1–200 μM, with a detection limit of 0.07 μM. The proposed method was facile, sensitive, and fast for DA detection with simple operation. DA in real serum samples was successfully detected with satisfactory results. Significantly, this fluorescent probe was used to fabricate paper-based test strips for visual detection of DA for the first time, which validated the potential on-site application.

•3-Aminobenzeneboronic acid functionalized Mn2+-doped ZnTe/ZnSe quantum dots were prepared.•The fluorescence intensity of APBA-dQDs was related linearly to the concentration of F– in the range of 0.25–1.5 µmol/L.•The proposed methodology for the sensing of F– in MC3T3-E1 osteoblastic cells was demonstratedIn this paper, 3-aminobenzeneboronic acid functionalized Mn2+-doped ZnTe/ZnSe quantum dots (APBA-dQDs) were prepared. The APBA functional groups had strong binding ability with F–, resulting in the quenchment of dQDs photoluminescence (PL). Under the optimal condition, the fluorescence intensity of APBA-dQDs was related linearly to the concentration of F– in the range of 0.25–1.5 µmol/L with a detection limit of 0.1 µmol/L. The selectivity of fluorescence quenching of APBA-dQDs for F– was enhanced. Moreover, the proposed methodology for the sensing of F– at EM 560 nm in MC3T3-E1 osteoblastic cells was demonstrated and got a satisfactory results. The results indicate that the APBA-dQDs are promising candidates for intracellular in MC3T3-E1 osteoblastic cells. To the best of our knowledge, it was the first report of F– sensing by using the quenched fluorescence of APBA-dQDs in non-cancerous cells.

In this paper, novel approaches for the synthesis of Type-II core/shell quantum dots (ZnTe/ZnSe QDs) and Mn2+-doped Type-II core/shell quantum dots (Mn:ZnTe/ZnSe QDs) with mercaptopropionic acid (MPA) as stabilizer were proposed. To our knowledge, it is the first time that both core/shell and doping synthesis methods are employed together to prepare photoluminescent Type-II core/shell Mn:ZnTe/ZnSe QDs in aqueous phase. The results show that the photoluminescence (PL) character of ZnTe/ZnSe QDs significantly changed with the doping of Mn2+. Furthermore, the fluorescence color of the QDs ranged over an extended emitting wavelength from blue to orange. Also, an increased PL quantum yield (from 5.3% to 7%) was obtained. The effects of the experimental conditions for synthesis and the PL emission properties were investigated in detail. The simple synthetic routes and improved optical properties make these QDs excellent probes for various strategies in chemo/biosensing and bioimaging.

In this work, a facile photoluminescence (PL) modulated nanosensor was designed for sulfite detection. The nanosensor was based on the different quenching effects of Fe3+ and Fe2+ on the PL intensity of nitrogen-doped graphene quantum dots (N-GQDs). Firstly, the PL of N-GQDs was quenched with the addition of Fe3+ due to the strong selective coordination between the N-GQDs and Fe3+. At the PL recovery step, Fe3+ can be transformed to Fe2+ with the addition of sulfite. Because Fe2+ had no apparent quenching effect on N-GQDs, the PL signal of N-GQDs can be enhanced largely. Under optimal conditions, the PL of N-GQDs displayed a good linear relationship versus the concentration of sulfite in the range of 4.0–200.0 μM. The limit of detection was 1.43 μM. This was the first time that sulfite detection had been based on the PL modulation of N-GQDs. The proposed method was facile, sensitive and fast for sulfite detection with simple operation and materials and sulfite in real water samples was successfully detected with satisfactory results. Furthermore, the sensing application range of N-GQDs has been extended based on this novel concept.

•We discuss the performance of silica-nanobead-based sensors.•We outline functionalization for silica-nanobead-based sensing systems.•We review analytical strategies for silica-nanobead-based sensors.•We highlight advances and future trends in silica-nanobead-based sensors.Silica-nanobead-based sensing systems have been developed and employed in various analytical and bioanalytical applications due to their attractive features, such as ideal modifiable surface, effective combining capacity with other nanomaterials, and good biocompatibility. The typical construction of silica-nanobead-based sensors includes the preparation of silica nanobeads and is followed by surface-chemistry modifications. In this review, we first cover the synthesis methods of different kinds of silica nanobeads in detail. We discuss the critical functional strategies for silica-nanobead-based sensing systems. This article also reviews silica-nanobead-based sensing and biosensing technologies, and highlights recent advances of representative examples with different sensing concepts. Finally, we conclude with a perspective on the opportunities and the challenges facing silica-nanobead-based sensors for further developments in this research field.

•A novel nanosensor based on water-soluble Mn-doped ZnTe/ZnSe QDs is prepared.•The nanosensor can be applied to the determination of phosphate in real sample.•This is the first report that Cd-free Mn2+-doped ZnTe/ZnSe QDs prepared in aqueous phase have been used in chemical sensing.Herein, the facile method with high selectivity for phosphate ion (Pi) sensing using novel Type-II core/shell Mn: ZnTe/ZnSe quantum dots (QDs) was reported. This was the first time that Mn: ZnTe/ZnSe QDs with highlighted optical properties were used for sensing. The water-soluble Mn: ZnTe/ZnSe QDs with a high quantum yield of 7% were synthesized by aqueous synthetic method. Compared with traditional ZnSe QDs or Mn: ZnSe QDs, the smaller effective band gap, longer wavelength and lower ionization potential (high valence band edge) for effective hole localization made Type-II core/shell Mn: ZnTe/ZnSe QDs to be stable and had high photoluminescence (PL). Only Mg2+ was found to be able to enhance Mn: ZnTe/ZnSe QDs PL selectively. The mechanism of fluorescence enhancement was attributed to the passivated surface nonradiative relaxation centers of Mn: ZnTe/ZnSe QDs. In the presence of Pi anion, the PL intensity got quenched due to the aggregation species of QDs via electrostatic attraction between Pi and Mg2+ on the surface of Mn: ZnTe/ZnSe QDs. Therefore, the quenching effect can be used to detect Pi selectively. The PL was observed to be linearly proportional to the Pi analyte concentration in the range from 0.67 to 50.0 μmol/L, with a detection limit of 0.2 μmol/L (S/N=3). The novel “on–off” fluorescence nanosensor for Pi detection was sensitive and convenient in the real analysis application. The reported analytical method of Mn: ZnTe/ZnSe QDs is highly sensitive and selective, which can corroborate the extension of its usages in chemo/ biosensing and bioimaging.The novel Mg2+–Mn: ZnTe/ZnSe QDs nanosensor for Pi detection.

•This proposed Zn2+–CMCS-QDs based sensor for lysozyme is ultrasensitive.•The selectivity and stability of the sensing system was improved than before.•The fluorescence “turn on–off” nanosensor is a novel nano-sensing model.In this work, we developed an ultrasensitive “turn on–off” fluorescence nanosensor for lysozyme (Lyz) detection. The novel nanosensor was constructed with the carboxymethyl chitosan modified CdTe quantum dots (CMCS-QDs). Firstly, the CMCS-QDs were fabricated via the electrostatic interaction between amino groups in CMCS polymeric chains and carboxyl groups on the surface of QDs. In the fluorescence “turn-on” step, the strong binding ability between Zn2+ and CMCS on the surface of QDs can enhance the photoluminescence intensity (PL) of QDs. In the following fluorescence “turn-off” step, the N-acetyl-glucosamine (NAG) section along the CMCS chains was hydrolyzed by Lyz. As a result, Zn2+ was released from the surface of QDs, and the Lyz–QDs complexes were formed to quench the QDs PL. Under the optimal conditions, there was a good linear relationship between the PL of QDs and the Lyz concentration (0.1–1.2 ng/mL) with the detection limit of 0.031 ng/mL. The developed method was ultrasensitive, highly selective and fast. It has been successfully employed in the detection of Lyz in the serum with satisfactory results.