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Long wavelength (i.e., orange- to red-light) fluorescence emission and functionality are critically longing for the development and applications of carbon dots (CDs) toward biosensor and bioimaging analysis. Herein, the N-doped carbon dots (N-CDs) with bright orange fluorescence emission at 592 nm were facilely synthesized via p-phenylenediamine as a carbon precursor by microwave method. The as-prepared N-CDs exhibit favorable biocompatibility, excellent water solubility, highly optical stabilities and display sensitive pH response behavior. When the pH is decreased from 9.45 to 2.45, its emission fluorescence intensity will be significantly enhanced. The pKa value of N-CDs is 5.80 and it shows linear response to the physiological pH range of 4.45–7.00. Moreover, the N-CDs also possess high selectivity of hydrogen ions over common metal ions and some bioactive molecules, excellent photostability and reversibility. Based on this, a fluorescence sensing platform is established for the detection of pH in the environment. The N-CDs were successfully used as the fluorescent probe for cellular imaging and applied to monitor pH fluctuations in live cells based on its biocompatibility and cell membrane permeability. It is also anticipated that the N-CDs are potential bio-nano-materials for real-time tracking of the intracellular pH especially under physiological conditions in the disease diagnosis, biosensing and biomedical fields. [ABSTRACT FROM AUTHOR]

Benefiting from the excellent photostability and biocompatibility, fluorescent nanoclusters have recently emerged as a highly attractive bio-sensing and imaging material, especially in early diagnosis of cancer. However, their clinic applications were limited by the unsatisfactory specificity and the complex synthesis. In this study, novel methionine coated gold nanoclusters (Met-AuNCs) have been prepared via an easily-achievable one-pot synthetic method. The prepared Met-AuNCs showed high imaging-specificity: after incubating with Met-AuNCs for 1 h, cancer cells (including A549, Hela, MCF-7, HepG2) were fluorescent, while the normal cells (WI-38 and CHO) showed no fluorescence. According to a series of controlled experiments, the reason for the high imaging-selectivity was proposed to originate from the specific recognition of L-type amino acid transporter overexpressed in cancer cells. [ABSTRACT FROM AUTHOR]

A hydrothermal synthetic approach is developed for the preparation of graphitic carbon nitride quantum dots (g-C 3 N 4 QDs) from human urine. The reported synthetic method is green, simple, low-cost, less time-consuming, and can be used for the large-scale production of the g-C 3 N 4 QDs. The as-prepared g-C 3 N 4 QDs possess a high quantum yield of 15.7% by using quinine sulfate as a reference, and display excitation-wavelength dependent fluorescent emission. In addition, the g-C 3 N 4 QDs exhibit high photostability, low cytotoxicity. and are successfully used as fluorescent probes for cell multicolor imaging. It is believed that the valuable nanomaterials, g-C 3 N 4 QDs, which are transformed from the human bodily wastes, are promising in diverse chemical applications. [ABSTRACT FROM AUTHOR]

Development of thiol-specific fluorescent probes with selectivity in different thiol compounds is more practical and significant than those without that capacity. In this work, a new quinoline-derived fluorophore, hydroxyl-substituted quinoline-benzo[ d ]oxazole 6 with high fluorescence quantum yield is synthesized and esterified with acrylic acid to afford two fluorescent probes, BQA-1 and BQA-2 for selectively discriminating Cys from Hcys/GSH based on conjugate addition-cyclization mechanism. BQA-1 exhibits a large ratiometric fluorescence response toward Cys in aqueous pH 7.4 solution with big emission peak-shifting from 383 nm to 518 nm, over 130 nm. The detection limit is determined to be as low as 0.59 μM. In contrast to BQA-1 , BQA-2 whose acrylic ester moiety is further modified with pyridine group, displays a turn-on fluorescence response to Cys with detection limit of 0.98 μM. Both BQA-1 and BQA-2 have relatively weak response to another two biothiols, Hcys and GSH and nearly no response to other nucleophiles. Furthermore, the potential application for the detection of biothiols in living cells has been demonstrated by cell imaging experiment. [ABSTRACT FROM AUTHOR]

Protein-encapsulated gold nanoclusters (Au NCs) have recently gained much attention in biosensing and bioimaging applications owing to their remarkable fluorescence properties, nontoxicity and good biocompatibility. In this work, the mannose was grafted onto the bovine serum albumin (BSA) encapsulated Au NCs (BSA-Au NCs) to produce a mannose functionalized BSA-Au NCs (Man-BSA-Au NCs) as a new fluorescence probe for Concanavalin A (Con A) detection and human breast cancer cell imaging. A new strategy with mannose-BSA conjugates as template was firstly applied for the synthesis of Man-BSA-Au NCs, leading to a high loading of mannose (767.6 ± 7.2 mg/L) onto BSA-Au NCs. The as-prepared Man-BSA-Au NCs showed advantages of facile preparation, good monodispersity and strong red-emission. Notably, aggregation-induced fluorescence quenching of Man-BSA-Au NCs was triggered by Con A due to the multivalent cooperative interactions between mannose and Con A, which was subsequently confirmed by MALDI-TOF MS. Hence highly selective and sensitive fluorescence detection of Con A was achieved by using Man-BSA-Au NCs as a fluorescence sensor. A good linear relationship was obtained over the range of 0.01–1 μM (R2 = 0.994) with a detection limit of 0.62 nM (S/N = 3). The developed sensor was then applied to determine Con A in human serum with acceptable recoveries of 93.70–104.8%. Moreover, based on the specific recognition between mannose and overexpressed mannose receptors on human breast cancer cells, the Man-BSA-Au NCs were successfully utilized for cancer cell imaging with good specificity. Image 1 • Man-BSA-Au NCs with high mannose loading were facilely prepared with new strategy. • Con A triggered an aggregation-induced "fluorescence quenching" of Man-BSA-Au NCs. • Man-BSA-Au NCs showed good sensitivity and selectivity for Con A sensing. • Man-BSA-Au NCs showed good specificity for human breast cancer cell imaging. [ABSTRACT FROM AUTHOR]

In this paper, silver nanoclusters (AgNCs) were synthesized by one facile, low-cost and green method with histidine acting as the stabilizer and ascorbic acid performing as reducing agent. AgNCs displayed excellent fluorescence property and good biocompatibility and were further functionalized by β-cyclodextrin (CD-AgNCs) for the highly sensitive detection of alkaline phosphatase (ALP) activity. ALP catalyzed the dephosphorylation of p -nitrophenylphosphate (NPP) to produce p -nitrophenol (NP), and NP can effectively quench the fluorescence of CD-AgNCs via the inner filter effect (IFE) due to the UV–vis absorption spectrum of NP had considerable overlap with the excitation spectrum of CD-AgNCs. Benefiting from the IFE and the host-guest interaction between CD and NP, this CD-AgNCs based system for ALP activity analysis displayed a good linear range of 0.02–10.0 U L−1 and the detection limit as low as 0.0046 U L−1. In addition, this proposed strategy also showed satisfactory performance for ALP analysis in human serum samples and bioimaging of intracellular ALP in living cells, indicating the great application prospect of this system for ALP activity analysis in medical related researches. AgNCs were facilely synthesized and further functionalized by β-cyclodextrin and performed as excellent fluorescent probes for ultrasensitive analysis of ALP and bioimaging intracellular ALP in living cells. Image 1 • AgNCs were synthesized by a one-step method and further modified with β-cyclodextrin. • Results indicated AgNCs displayed good fluorescence property and biocompatibility. • CD-AgNCs were applied as excellent fluorescent probes for ALP analysis. • Integrating IFE and host-guest recognition, ultrasensitive ALP sensing was conducted. • The approach was applied for ALP sensing in human serum and bioimaging in cells. [ABSTRACT FROM AUTHOR]