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Specific staining of cancer cells is momentous for cancer research. Nanoprobe with multivalent recognition is emerging as powerful tools for bioimaging, but the nonspecific cell uptake and complex functional modification procedures are still obstacles for specific detection and convenient synthesis. Carbon dots (CDs) with an intrinsic targeting ability, excellent optical properties and biocompatibility acquired from an efficient one-step fabrication procedure were urgently desired in specific cancer cells visualization. Herein, inspired by the interrelationships between interface and biomolecular mechanisms, we suggested that it was possible to construct CDs with the desired characteristics for folate receptor (FR) positive-expressed cancer cell imaging via rich hydroxyl groups Tris-assisted one-step hydrothermal treatment of folate acid (FA) and l -Arginine (L-Arg) precursors. The prepared small-sized F-CDs were equipped with abundant hydroxyl, pterin and negative charge surface, and possessed environmental friendliness, outstanding photostability and biocompatibility. Moreover, F-CDs had an intrinsic FR positive-expressed cancer cell targeting ability without any post-modification of the ligands. Rich hydroxyl groups play a vital role in endowing the optical properties and biological effects of F-CDs. F-CDs could be used as a promising candidate for FR-expressed cancer cell labeling and tracking. In addition, the caveolae-mediated endocytosis pathway of F-CDs was ascertained. More importantly, experimental results confirmed that the combination of physicochemical properties may provide an efficient strategy to overcome non-specific cell uptake interactions for cell labeling. Our strategy put forward a promising alternative to design fluorescent CDs for extensive chemical and biomedical applications. Tris-assisted one-step fabrication of functional F-CDs for specific folate receptor positive-expressed cancer cell imaging. [Display omitted] • F-CDs were fabricated via rich hydroxyl groups Tris to mediate hydrothermal process of FA and L-Arg. • Rich hydroxyl groups of Tris play a vital role in the optical properties and intrinsic targeting ability for FR positive-expressed cancer cell for labeling and tracking. • This study provides an efficient strategy to design fluorescent CDs for extensive applications. [ABSTRACT FROM AUTHOR]

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]

Fluorescent carbon nanoparticles (FCNPs) have been deeply researched and widely applied in recent years due to their good optics performance, chemical stability and biocompatibility. Herein, a green and rapid microwave-assisted solid-phase synthesis (solvent-free) approach was proposed for the fabrication of highly FCNPs in a very short period of time, 4 min. The as-prepared FCNPs can emit a blue emission with quantum yield of up to 63.2% in water solution and show yellow fluorescence in the solid state. The FCNPs also exhibit special solvent effect that the fluorescence emission can be adjusted by controlling the solvent ratio of ethanol and water. Most importantly, the FCNPs possess a narrow-range pH response. The probe responds linearly and rapidly to minor pH fluctuations within the range of 3.47–5.10 and the correlation coefficient is above 0.99. The proposed FCNPs also exhibit high photostability and reusability. As expected, the cell imaging and intracellular pH monitoring was achieved successfully in living SMMC 7721 hepatoma cells by this probe. The FCNPs is promising as a convenient and general fluorescent pH sensor for bioimaging 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]

We herein opened up a facile and green strategy for the fabrication of bright orange-fluorescent gold−silver nanoclusters (AuAgNCs@ew, GSNCs) by a one-pot synthesis at a vital molar ratio of Au/Ag precursors in the egg white protein matrix using microwave-assisted method. The prepared GSNCs exhibited enhanced fluorescence with fluorescent quantum yield of 5.4%, which is dependent on gold and silver synergies. Due to the advantageous superiority of low-toxicity, excellent stability and satisfactory fluorescence, the as-prepared GSNCs has been successfully used in cell imaging and temperature sensing. More strikingly, the GSNCs emerged strong response to CN − with rapid, selective, and ultrasensitive characteristics. The detection limit was approximately 138 nM, which is nearly 20 times lower than the maximum level (2700 nM) of CN − in drinking water set up by the World Health Organization (WHO). In addition, the as-prepared GSNCs could be applied to detecting real samples with minimum interference. Our findings showed that this new GSNCs probe is eco-friendly and large-scale development for potential applications including the detection of environmental pollution and bioimaging. [ABSTRACT FROM AUTHOR]

The facile and noninjurious image of cells with high resolution and low toxicity is essential since imaging can offer rich and direct information and insights into metabolic activities, clinical diagnosis, drug delivery and cancer therapy. In this contribution, a smart imaging probe was employed as a contrast agent for dark-field cell imaging. Au core/Ag shell nanorods (Au@Ag NRs) that characterized by X-ray diffraction and X-ray photoelectron spectroscopy, formed Au@Ag@AgI NRs when exposed to iodine, which greatly enhanced the light scattering of nanorods. Herein, the silver shell acted as the response element for iodine as well as the protective agent for Au core. When conjugated with folate, the nanorods can be used to image human cervical cancer cells (HeLa cells) under a dark-field microscope. Nanorods were demonstrated with excellent tumor cellular uptake ability without obvious cytotoxicity, making them ideal candidates in biosensing and bioimaging applications. Nanorods were restructured with iodine to enhance the light scattering for cell imaging, making them ideal candidates in bioimaging applications. [Display omitted] • The light scattering of AuNRs has been greatly enhanced for cell imaging. • The iodine-induced restructuring of Au@Ag NRs is highly specific among inorganic ions and biological macromolecules. • Nanorods with strong light scattering can enter cells readily, making them potentially useful as contrast agents. • Silver coating acted as the response element for iodine as well as the protective agent for AuNRs to avoid exposure to iodine. [ABSTRACT FROM AUTHOR]

The fluorescent probe, GXY-ADP-2, with xanthene structure as the fluorescent core was designed and prepared for the selective detection of peroxynitrite (ONOO−). ONOO− can be produced endogenously and exogenously and is a strong oxidant with a short half-life. Oxidative modifications of biomolecules, that can be attributed to the formation of ONOO−, occur in the reactions of biomolecules with secondary ONOO−-derived radical oxidants. Therefore, it is very important to develop a specific fluorescent probe for detecting ONOO− to monitor oxidative stress state. The excitation wavelength and emission wavelength of the probe are 689 nm and 739 nm respectively. In the process of co-incubation with ONOO−, generate a new substance with two internal conjugated structures through a special reaction mechanism, one giving the fluorescence with the excitation wavelength of 347 nm and the emission wavelength of 484 nm with the detection limit of 0.12 μM, and the other that with the excitation wavelength of 433 nm and the emission wavelength of 583 nm with the detection limit of 0.077 μM. The linear dynamic range of the probe is 0–5 μM. Its response is not affected by the other reactive oxygen species, thus can sensitively detect ONOO−. In bioimaging experiments with HepG2 cells, the green and blue cell fluorescence signals (583 nm and 433 nm, respectively) were increased, while the red one (739 nm) was significantly reduced, under lipopolysaccharide (LPS) induced oxidative stress, proving that the probe could sensitively detect ONOO− in living cells. This work provides a new tool for the dynamic changes of ONOO− and oxidative stress processes in biological systems. [Display omitted] • A new fluorescent probe, GXY-ADP-2, was developed for detection of ONOO−. • GXY-ADP-2 exhibited high specificity and sensitivity to ONOO−. • GXY-ADP-2 is a ratiometric fluorescent probe with three-channel fluorescence signal changed. • GXY-ADP-2 can detect the dynamic change of ONOO− in living cells. [ABSTRACT FROM AUTHOR]

Development of noninvasive bioimaging fluorescent probes for detecting particular enzyme activity is greatly recommendable for preclinical diagnosis of cancer. Given that the elevated β-gal activity is positively correlated with several tumors, developing a fluorescent probe for the sensing of β-gal is therefore highly desirable for cancer diagnosis. Herein, a new enzyme-activatable near-infrared (NIR) turn-on fluorescent probe (DMC-βgal) was developed for accurately detecting β-gal activity characterized by excellent selectivity, high sensitivity (LOD = 0.298 U/L), and low toxicity. More importantly, DMC-βgal qualifies remarkable NIR excitation (725 nm) and emission wavelength (770 nm), an ideal tool for restrained photodamage and suppressed autofluorescence. The above excellent performance of DMC-β-gal allowed for the accurate monitoring of endogenous β-gal in living cells. Moreover, the probe was successfully applied to detect intracellular β-gal activity in different types of cancer cells, verifying that SKOV-3 cells had a higher level of β-gal activity than those of A549, HCT-116, MCF-7, and HepG2 cells. Furthermore, DMC-βgal could real-time visualize endogenously β-gal in tumor-bearing nude mice with low auto-fluorescence interference. All results fully demonstrated that DMC-βgal has potential value as a promising strategy for diagnosis of β-gal-related diseases. [Display omitted] • A new near-infrared excited and emitted β-galactosidase (β-gal) fluorescent probe DMC-βgal was synthesized. • The probe DMC-βgal is characterized by excellent selectivity and high sensitivity (LOD = 0.298 U/L). • The probe is applied to prove that the β-gal activity in SKOV-3 cells is higher than HepG2, A549, HCT-116, MCF-7 cells. • DMC-βgal can real-time visualize the β-gal activity in tumor-bearing nude mice with low photodamage and autofluorescence. [ABSTRACT FROM AUTHOR]

According to the mechanism of hydrazine to ester bond elimination, a novel ratiometric fluorescent probe (FCP) based on the fluorescein-coumarin structure is designed and synthesized for detecting hydrazine. The obvious red shift in the absorption and fluorescence spectrum is caused by the hydrolysis of the ester bond of FCP by upon mixing with hydrazine. The proposed FCP probe is shown to have linear detection ranges from 0 to 250 nM for hydrazine, and LOD is 0.364 nM. In addition, this promising probe possesses high sensitivity and selectivity for monitoring the intracellular hydrazine, thus, has great potential to be applied in early diagnosis of disease. Meanwhile, it has been successfully applied to the detection and cell imaging of hydrazine in actual water samples. Image 1 • The fluorescence sensing is realized by hydrolysis of the ester bonds of the probe. • The probe shows high selectivity and sensitivity toward hydrazine over other structural analogs and reductive species. • FCP is a ratiometric fluorescent probe that can be used for visual inspection of hydrazine. • The probe affords remarkable red shifts in the absorption and fluorescence spectra upon treating with hydrazine. • Abstract. [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]

A novel ratiometric emission N, S dual-doped carbon dots (N, S-CDs) were facilely developed for pH visual sensing via one-step hydrothermal method. The proposed N, S-CDs displayed intrinsic pH-sensitive behavior and exhibited ratiometric fluorescence emission (F 563 nm /F 645 nm) characteristic with the variation of pH values. Interestingly, a significant red shift of emission wavelength can be observed at 645 nm along with the emission at 563 nm decreased accordingly when the pH changed from 3.0 to 1.0. Simultaneously, the fluorescence of N, S-CDs aqueous solution was visually varied from yellow to red. The ratiometric pH linear response was in the region of 3.6 to 2.4 and the pK a was 2.90. Moreover, the N, S-CDs hold unique optical properties, good reversibility, superior biocompatibility and low cytotoxicity, which was further employed to monitor the intracellular pH fluctuations through the visible fluorescence changes between yellow and red. All these findings demonstrated that N, S-CDs can be utilized as the visual biosensor platform for tracking pH variations in extremely acidic environments such as gastric juice, which provided novel insights for clinical medical disease diagnosis (e.g., stomach disease detection) and other biomedical fields. Image 1 • The novel fluorescent N,S dual-doped carbon dots (N,S-CDs) for ratiometric and visual pH sensing were proposed via one-step hydrothermal method. • N,S-CDs displayed intrinsic pH-dependent behavior and exhibited ratiometric fluorescence emission (F 563 nm /F 645 nm) feature with the variation of pH. • Outstanding performance of the N,S-CDs with superior biocompatibility, high photostability, low toxicity and favorable cellular labeling capability. • The N,S-CDs can implemented as a fluorescent visualization biosensing platform for ratiometric monitoring pH fluctuations in extremely acidic environments. [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]