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Pathogenic bacteria, as a major cause of foodborne diseases, pose a serious threat to human health, which urges the development of sensitive and accurate detection methods. Herein, a fluorescent genosensor was designed for Staphylococcus aureus (S. aureus) detection based on fluorescent probes and graphene oxide quantum dots (GOQDs). The π-π stacking and hydrogen bond interactions between GOQDs and specific single-stranded DNA (ssDNA) of the fluorescent probes were exploited by the developed genosensor. The interactions brought the GOQDs to the surface of the fluorescent probes, quenching strong upconversion fluorescence. However, the hybridization of the recognition probes anchored on the fluorescent reporters with complementary nuc target obstructed the interactions, causing the fluorescence to gradually increase with the increasing concentration of complementary nuc target. Consequently, the target-specific sensor exhibited high sensitivity with a LOD of 0.98 × 10−17 mol L−1 and a linear range from 1 × 10−17 to 1 × 10−11 mol L−1. Moreover, the genosensor was successfully applied for real sample analysis with excellent recoveries. Significantly, the sensor could be used for the detection of other pathogens in actual samples by replacing recognition probes and primers. [Display omitted] • A fluorescent genosensor was developed for sensitive and accurate detection of Staphylococcus aureus. • Water-soluble UCNPs were prepared and modified with specific nuc ssDNA as fluorescent probes. • FRET based on the fluorescent probes and GOQDs was used. • Under the optimized condition, a 0.98 × 10−17 mol L−1 LOD was achieved. • It could be used for the detection of other pathogens in actual samples by replacing recognition probes and primers. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A new N-oxide based and turn on fluorescent probe for Fe2+ was developed. • The probe possessed a high selectivity for Fe2+ among various biologically relevant species and fast rapid response. • Monitoring Fe2+ with TPM fluorescence imaging for the first time. Abstract Iron is an essential element for human body, involved in important biochemical processes in the body, especially in biological oxidation. Misregulation of iron levels in the cell is concerned with serious diseases. Here, a novel two photon and turn on NIR-fluorescent probe based ICT for detection of Fe2+ is first reported. The probe exhibited brilliant selectivity and excellent sensitivity (DL = 4.5 μM), rapid response (15 min) and "naked-eye colorimetric sensor" for monitoring of Fe2+. More importantly, the probe was successfully applied to real-time monitor Fe2+ in living cell through two-photon microscopy fluorescence imaging with excitation 680 nm. [ABSTRACT FROM AUTHOR]

Graphical abstract Two-Photon Fluorescent Probe TP-1Bz was developed for dual-targeting ratiometric viscosity and peroxynitrite in living cells and tissue. Highlights • Two-photon fluorescent molecule TP-1Bz was designed with near infrared emission, water solubility and cell penetrability. • TP-1Bz showed good mitochondria targeting capability and high sensitivity to the viscosity change in mitochondria. • TP-1Bz proved to detect the exogenous and endogenous ONOO– in mitochondria, even in tissue samples of rat liver. Abstract The irregular viscosity and peroxynitrite (ONOO–) concentration in mitochondria would result in mitochondria disorders. However, fluorescent probes that can detect both of viscosity and peroxynitrite have not been explored. For this reason, a two-photon fluorescent molecule TP-1Bz was designed and synthesized in this work for the dual-ratiometric-imaging of viscosity and exogenous and endogenous ONOO– in mitochondria. Results indicated that TP-1Bz has two emissions at 407 nm and 650 nm respectively, their ratio (I650/I407) showed linear relationship to the viscosity of the media in the logarithmic plot, and its two-photon action cross-section (Φσ) at 880 nm was increased from 1.2 GM in aqueous solution to be 86.3 GM (72-fold) in 99% glycerol. With a good targeting capability to mitochondria, TP-1Bz allowed us to measure the average viscosity in the mitochidria of HepG2 cells (73.3 cp) and the mitochondria viscosity change upon the addition of ionpores. TP-1Bz also showed the high sensitivity to ONOO– (LOD close to 12.1 nM) in water/glycerol (2/3) solvent as well as the high selectivity over other ROS. With the advantages of its lower cytotoxicity, pH- and photo- stabilities, TP-1Bz was successfully employed for imaging ONOO– in living cells and even in tissue samples of rat liver through the monitoring the emission intensities of the blue and red channels. As the first example of two-photon ratiometric fluorescent probe for dual-imaging viscosity and peroxynitrite in mitochondria, TP-1Bz has great potential to be developed for clinical applications. [ABSTRACT FROM AUTHOR]