•Carbon dots (CDs) were prepared from carrot as new carbon source.•The CDs modified with polyethyleneimine and nile blue were used for a ratiometric two-photon fluorescence probe.•The probe enabled highly efficient detection of S2- in real biological fluids.In this article, a facile and green synthesis of carbon dots (CDs) was developed by using natural carrot as new carbon source. After direct hydrothermal carbonization for 5 h at 180 °C, CDs were prepared facilely. Then, CDs were conjugated with polyethyleneimine (PEI) and Nile Blue (NB) chloride to produce CDs/PEI/NB nanocomposites under electrostatic interactions. Upon excitation at 800 nm, two-photon fluorescence (TPF) of the nanocomposites was observed, with TPF peaks of CDs at 415 nm and NB at 675 nm. The addition of Cu2+ could lead to TPF quenching of CDs via inner filter effect, but hardly any impacted on TPF of NB. Afterward, the added S2- combined with Cu2+ to form stable species that caused the separation of Cu2+ from CDs surface and the TPF recovery of CDs, with negligible effects on TPF of NB. Herein, a new CDs-based ratiometric TPF turn-on probe of S2- was developed and showed a good linear relationship (R2 =0.9933) between ratiometric TPF intensity (I415/I675) and S2- concentration (0.1–8.0 μM), with a low detection limit of 0.06 μM. This probe was highly selective and sensitive toward S2- over potential interferences in real biological fluids, with high detection recoveries.Download high-res image (181KB)Download full-size image

•Mn2+:ZnS@SiO2/MoS2-RBS nanocomposites were developed as a novel ratiometric two-photon excited fluorescence probe.•This probe could conduct real-time detection of nitric oxide release in situ.•High feasibility of this probe was confirmed in tumor intracellular microenvironments.Probe-donor integrated nanocomposites were developed from conjugating silica-coated Mn2+:ZnS quantum dots (QDs) with MoS2 QDs and photosensitive nitric oxide (NO) donors (Fe4S3(NO)7−, RBS). Under excitation with near-infrared (NIR) light at 808 nm, the Mn2+:ZnS@SiO2/MoS2-RBS nanocomposites showed the dual-emissive two-photon excited photoluminescence (TPEPL) that induced RBS photolysis to release NO in situ. NO caused TPEPL quenching of Mn2+:ZnS QDs, but it produced almost no impact on the TPEPL of MoS2 QDs. Hence, the nanocomposites were developed as a novel QDs-based ratiometric TPEPL probe for real-time detection of NO release in situ. The ratiometric TPEPL intensity is nearly linear (R2 = 0.9901) with NO concentration in the range of 0.01∼0.8 μM, which corresponds to the range of NO release time (0∼15 min). The detection limit was calculated to be approximately 4 nM of NO. Experimental results confirmed that this novel ratiometric TPEPL probe possessed high selectivity and sensitivity for the detection of NO against potential competitors, and especially showed high detection performance for NIR-light triggered NO release in tumor intracellular microenvironments. These results would promote the development of versatile probe-donor integrated systems, also providing a facile and efficient strategy to real-time detect the highly controllable drug release in situ, especially in physiological microenvironments.

•Highly luminescent Ag2Te quantum dots (QDs) were prepared using glycerol as viscous solvent.•Ag2Te QDs exhibited tunable near-infrared photoluminescence (PL) emission and high PL quantum yields.•The QDs were favorably used for targeted PL imaging of tumor cells.In this work, highly luminescent and emission tunable Ag2Te quantum dots (QDs) were facilely prepared by using water-dispersed glycerol as viscous solvent and CH3COOAg/Na2TeO3 as Ag/Te precursors. Viscous glycerol was utilized to slow the nucleation and growth of QDs at 200 °C, and enabled the isolation of QDs with different emission wavelengths. Experimental results revealed that the as-prepared Ag2Te QDs exhibited tunable near-infrared emission from 930 to 1084 nm, high photoluminescence (PL) quantum yields (QYs, more than 20%), good photostability and low cytotoxicity. After surface coating of a thin silica shell (∼1.4 nm), the resulting NH2 terminated Ag2Te@SiO2-NH2 displayed enhanced PL QYs, higher photostability and biocompatibility when compared with the original Ag2Te QDs. Through a facile carboxy-amine coupling, folic acid (FA) was grafted with Ag2Te@SiO2-NH2 to form Ag2Te@SiO2-FA nanocomposites, which were used for targeted PL imaging of folate receptor over-expressed tumor cells.

•This review reports the recent advances on carbon nanomaterials (CNMs)-based electrochemical aptasensors (ECASs).•Different CNMs and CNMs-composites are involved.•Applications of CNMs in ECASs are summarized.•Future perspectives of CNMs-based ECASs are highlighted.Carbon nanomaterials (CNMs) have attracted increasing attention due to their unique electrical, optical, thermal, mechanical and chemical properties. CNMs are extensively applied in electronic, optoelectronic, photovoltaic and sensing devices fields, especially in bioassay technology. These excellent properties significantly depend on not only the functional atomic structures of CNMs, but also the interactions with other materials, such as gold nanoparticles, SiO2, chitosan, etc. This review systematically summarizes applications of CNMs in electrochemical aptasensors (ECASs). Firstly, definition and development of ECASs are introduced. Secondly, different ways of ECASs about working principles, classification and construction of CNMs are illustrated. Thirdly, the applications of different CNMs used in ECASs are discussed. In this review, different types of CNMs are involved such as carbon nanotubes, graphene, graphene oxide, etc. Besides, the newly emerging CNMs and CNMs-based composites are also discoursed. Finally, we demonstrate the future prospects of CNMs-based ECASs, and some suggestions about the near future development of CNMs-based ECASs are highlighted.

•This review addresses previous examples for synthetic methods of fluorescent colloidal silver chalcogenide quantum dots (QDs).•Then, it highlights the QDs’ significant applications.•Finally, it gives the perspectives on future exploration of the QDs’ synthetic methods and applications.Narrow bandgap colloidal semiconductor nanocrystals have attracted increasing attention in recent years and studies have demonstrated their significant applications in optics, electronics, biomedicine, materials science, and other areas. During the past decade, many studies have investigated colloidal silver chalcogenide (Ag2X, X = S, Se, Te) quantum dots (QDs) due to their numerous advantages, such as near-infrared (NIR) emission, ultralow toxicity, high photo-/colloidal stability, low cost, and facile synthesis. Compared with conventional NIR QDs (which contain heavy metal elements such as Cd, Hg, or Pb), NIR emissive Ag2X QDs avoid the intrinsic hazard of heavy metal ions and they have ultralow toxicity in biomedical applications. However, no previous review has summarized the synthetic methods and applications of Ag2X QDs in a systematic manner. In this review, we discuss previously reported synthetic methods and the advantages of directly synthesized and surface functionalized Ag2X QDs, as well as reporting their potential applications in bioimaging, chemo-/bio-detection, QD-sensitized solar cells, and photocatalysis, as well as antimicrobials and thermoelectric materials. Recent methods for synthesizing Ag2X QDs are discussed in detail. The unique optoelectronic properties of Ag2X QDs and their assemblies make these QDs excellent materials for a broad range of applications, and thus their assemblies and properties are highlighted. Finally, we suggest the future exploration of highly efficient synthetic methods and the potential application fields of Ag2X QDs.

Water-soluble multidentate polymer coated CdTe quantum dots (QDs) were prepared via a stepwise addition of raw materials in a one-pot aqueous solution under ambient conditions. Just by adjusting the compositions of raw materials, different sized CdTe QDs were achieved within a short time. The as-prepared QDs showed compact surface coating (1.6–1.8 nm) of polymer ligands and photoluminescence (PL) emitted at 533–567 nm, as well as high colloidal/photo-stability and quantum yields (58–67%). Moreover, these QDs exhibited significant upconversion luminescence (UCL) upon excitation using an 800 nm femtosecond laser. Experimental results confirm that the UCL was ascribed to the two-photon assisted process via a virtual energy state. Then, the two-photon excited QDs were further developed as a novel UCL probe of dopamine (DA) due to self-assembled binding of DA molecules with QDs via non-covalent bonding. As a receptor, the DA attached onto the QD surface induced an electron transfer from QDs to DA, triggering UCL quenching of QDs. This UCL probe of DA presented a low limit of detection (ca. 5.4 nM), and high selectivity and sensitivity in the presence of potential interferences. In particular, it was favorably applied to the detection of DA in biological fluids, with quantitative recoveries (96.0–102.6%).

A facile one-step method for preparing water-dispersible carboxylic acid-terminated AgInS2 quantum dots (QDs) with near-infrared (NIR) emission was developed. In the presence of polyethylenimine, the as-prepared AgInS2 QDs gathered together to form QDs-self-assemblies, followed by centrifugating to obtain QDs aggregates. After that, the resulting QDs aggregates were calcined at elevated temperature to yield AgInS2 nanospheres. Experimental results confirmed that the AgInS2 nanospheres exhibited a mesoporous structure and consisted of repeated units of AgInS2 QDs. The mesoporous AgInS2 nanospheres had photoluminescence (PL) in the visible region that was different from that of the original AgInS2 QDs emitted in the NIR region. High PL stability and low cytotoxicity of the nanospheres were verified experimentally. These results further revealed the potential of mesoporous AgInS2 nanospheres for biomedical application, especially serving as novel nanoprobes for in vitro and in vivo PL imaging.

•Mn2+-doped ZnSe QDs were combined with photosensitive NO donors (RBS).•The prepared nanocomposites of QDs-RBS presented marked two-photon excited fluorescence (TPEF).•The TPEF triggered NO releasing from RBS.•The released NO was used to kill cancer cells.In this paper, glutathione capped Mn2+-doped ZnSe quantum dots (QDs) were conjugated with nitric oxide (NO) photosensitive-donors (Fe4S3(NO)7−, RBS) to fabricate QDs-RBS nanocomposites under electrostatic interactions. The QDs-RBS presented marked two-photon excited fluorescence (TPEF, peaked at 570 nm) upon two-photon excitation (with 1130 nm laser). The TPEF emitting from QDs in QDs-RBS could trigger the RBS photolysis to release NO. By regulating excitation power and irradiation time, the QDs-RBS showed controllable NO release in water-soluble environments. Upon two-photon excitation, the QDs-RBS also demonstrated high growth inhibition to cancer cells. Experimental results revealed that the TPEF (570 nm) of QDs efficiently triggered the release of NO from RBS, and the released NO induced significant cytotoxicity to cancer cells.

•Non-fluorescent Fe3O4–CuFL–RBS nanocomposites were facilely prepared by electrostatic interactions.•The nanocomposites enabled releasing NO upon visible light irradiation.•The released NO could be detected in situ based on selective fluorescence turn-on response of nanocomposites to NO.Under electrostatic interactions, polyethylenimine-stabilized Fe3O4 magnetic nanoparticles were assembled with photosensitive nitric oxide (NO) donors (Fe4S3(NO7−))(Fe4S3(NO7−)), RBS) and CuFL complex consisting of fluorescein derivatives (FL) and CuII to prepare Fe3O4–CuFL–RBS nanocomposites. The as-prepared nanocomposites exhibited weak fluorescence and hardly any release of NO upon light irradiation of 480 nm. The nanocomposites enabled NO release due to RBS photolysis under 365 nm light irradiation, while the released NO could in situ conjugate with CuFL to form FL–NO complex based on N-nitrosate reaction, which was verified by fluorescence increase responses of FL–NO (excited at 480 nm). Thus, Fe3O4–CuFL–RBS nanocomposites realized light-triggered NO release and turn-on fluorescence detection of NO in situ.

•Ag2Te quantum dots (QDs) were prepared in ambient one-pot aqueous solution using multivalent polymers as stabilizers.•The QDs exhibited compact sizes, excellent photo-/colloidal stability, biocompatibility and high quantum yields.•The QDs were used for bioimaging in second near-infrared biological window.In this study, we described a facile ambient one-pot aqueous synthesis of fluorescent Ag2Te quantum dots (QDs) adopting multivalent polymers (poly(maleic anhydride) homopolymers) as stabilizers. In experiments, Ag2Te QDs were synthesized via a stepwise addition of the stabilizers, precursors (AgNO3/Na2TeO3) and promoters (NaBH4/N2H4·H2O) in ambient one-pot aqueous solution. By regulating the compositions of raw materials, water-dispersed Ag2Te QDs (3.8–4.7 nm) were achieved and exhibited tunable photoluminescence (PL) emission (995–1068 nm) in the second near-infrared (NIR-II) region, accompanying with the minimized surface coating thickness (1.5–1.9 nm). Such compact coating of multivalent polymers promoted PL emission of Ag2Te QDs, so showing high PL quantum yields (PLQYs: 13.1–15.2%). In addition to compact sizes and high PLQYs, experimental results testified that the Ag2Te QDs demonstrated high photo-/colloidal stability and ultralow cytotoxicity, which implied their promising applications, especially serving as an effective nanoprobe for bioimaging in the NIR-II biological window.

•A facile synthesis of pH-/near infrared (NIR) light-sensitive core/shell hybrid nanospheres was reported.•The nanospheres with unique advantages were developed toward a smart carrier for controlled drug release of 5-fluorouracil.•Experiments versified the synergistic effect of chem-photothermal therapy of nanospheres.We described a facile synthesis of pH and near-infrared (NIR) light dual-sensitive core/shell hybrid nanospheres, consisting of gold nanorods (GNR) as the core and poly(N-isopropylacrylamide-co-methacrylic acid) as the shell, p(NIPAM-MAA). The resultant GNR/p(NIPAM-MAA) nanospheres showed a core/shell structure, with an average diameter of ∼110 nm and a strong longitudinal surface plasmon band at NIR region. Due to the photothermal effect of GNR and pH/thermal-sensitive volume transition of p(NIPAM-MAA) hydrogels, the nanospheres with loading of 5-fluorouracil (5-FU) by electrostatic interactions were developed as a smart carrier for pH- and photothermal-induced release of 5-FU. Experimental results testified that the cumulative release of 5-FU from nanospheres was markedly increased in a mild acidic medium. Moreover, a NIR light (808 nm) irradiation triggered a greater and faster release of 5-FU, which was further testified by relevant results from in vitro cytotoxicity assay, in vivo tumor growth inhibition and histological images of ex vivo tumor sections. These results revealed significant applications of GNR/p(NIPAM-MAA) nanospheres in controlled release of anticancer agents and photothermal ablation therapy of tumor tissues, accompanied by synergistic effect of chem-photothermal therapy.

•Ag2S quantum dots/aptamer/5-fluorouracil hybrids were prepared by facile self-assembling.•The hybrids were developed as a novel near-infrared photoluminescence turn-on probe of CA125 antigen.•The probe enabled highly selective and sensitive detection of CA125 in real human body fluids.In this article, Ag2S quantum dots (QDs) were prepared by a facile aqueous synthesis method, using thiourea as a new sulfur precursor. Based on electrostatic interactions, 5-fluorouracil (5-Fu) was combined with the aptamer of CA125 antigen to fabricate aptamer/5-Fu complex. The surface of as-prepared Ag2S QDs was modified with polyethylenimine, followed by combination with the aptamer/5-Fu complex to form Ag2S QDs/aptamer/5-Fu hybrids. During the combination of Ag2S QDs with aptamer/5-Fu complex, near-infrared (NIR) photoluminescence (PL) of QDs (peaked at 850 nm) was markedly reduced under excitation at 625 nm, attributed to photo-induced electron transfer from QDs to 5-Fu. However, the addition of CA125 induced obvious NIR PL recovery, which was ascribed to the strong binding affinity of CA125 with its aptamer, and the separation of aptamer/5-Fu complex from the surface of QDs. Hence, the Ag2S QDs/aptamer/5-Fu hybrids were developed as a novel NIR PL turn-on probe of CA125. In the concentration range of [CA125] from 0.1 to 106 ng mL−1, there were a good linear relationship between NIR PL intensities of Ag2S QDs and Log[CA125], and a low limit of detection of 0.07 ng mL−1. Experimental results revealed the highly selective and sensitive NIR PL responses of this probe to CA125, over other potential interferences. In real human body fluids, this probe also exhibited superior analytical performance, together with high detection recoveries.