Simple NIR-Emitting ESIPT Fluorescent Probe for Thiophenol with a Remarkable Stokes Shift and Its Application

Rapid Detection of Bacterial Resistance to β-Lactam Antibiotics with a Relay-Response Chemiluminescence Assay

Bacterial resistance caused by β-lactamases has been a major threat to public health around the world, seriously weakening the efficacy of β-lactam antibiotics, the most widely used therapeutic agents against infectious diseases. To detect the bacterial resistance to β-lactam antibiotics, particularly specific type of β-lactam antibiotics, in a rapid manner, we report herein a relay-response chemiluminescence assay. This assay mainly consists of two reagents: a β-lactam-caged thiophenol and a thiophenol-sensitive chemiluminescence reporter, both of which are synthetically feasible. The selective hydrolysis of β-lactam by β-lactamase leads to the releasing of free thiophenol, which then triggers the emission of a chemiluminescence signal in a relay manner. Three thiophenol-caged β-lactams, structural analogues of cephalothin, cefotaxime, and meropenem, respectively, have been synthesized. And the application of this assay with these analogues of β-lactam antibiotics allows fast detection of β-lactamase-expressing resistant bacteria and, more impressively, provides detailed information on the resistant scope of bacteria.

Two red/blue-emitting fluorescent probes for quick, portable, and selective detection of thiophenol in food, soil and plant samples, and their applications in bioimaging

Thiophenol (PhSH), which is widely used in many industries, poses significant health risks owing to its acute toxicity and irritating effects. Thus, the detection of PhSH is crucial for ensuring environmental and food safety. There is significant room for improvement in the sensing properties of the reported analytical methods, such as response time, detection limit, selectivity, and portable detection. Herein, we present two new red/blue fluorescence-emissive sensors (NS1 and NS2) for PhSH detection. After reacting with PhSH, NS1 exhibited a low detection limit (66.7 nM), red emission, fast response time of just 10 s, and large Stokes shift (240 nm). NS2 could detect PhSH with a low detection limit (75.8 nM), fast response time of 20 s, and blue emission. The noticeable color response and portability of the two probes made them suitable for on-site detection of PhSH in various samples, such as water, soil, plant, food samples, and living cells. Moreover, it has been shown that these probes could be used to determine PhSH content in smartphone applications, thin layer chromatography kits, and polysulfone capsule kits. Prepared probes have low cytotoxicity and show good permeability in tested living cells, which is important for early diagnosis, disease research, and emergency analysis. Compared with other studies, the proposed approach has remarkable advantages in terms of detection limit, portability, response time, and low cytotoxicity. Thus, it meets the crucial demand for ensuring health, environmental and food safety, and adherence to regulatory standards.

ESIPT-based fluorescent enhanced probes prompted by methylated β-cyclodextrin for the detection of thiophenols

Thiophenol and its derivatives are compounds with high toxicity to organisms and environmental pollution, so it is necessary to detect the level of thiophenols in the environment and biological samples. The probes 1a-b were obtained by introducing the 2,4-dinitrophenyl ether group into diethylcoumarin-salicylaldehyde based compounds. And they can form host-guest compounds with methylated β-cyclodextrin (M-β-CD), the association constants of inclusion complexes are 49.2 M-1, 125 M-1 respectively. The fluorescence intensities of probes 1a-b at 600 nm (1a) and 670 nm (1b) increased significantly in thiophenols detection. Meanwhile, with the addition of M-β-CD, the hydrophobic cavity of M-β-CD significantly increased the fluorescence intensity of probes 1a-b, thus the detection limits of probes 1a-b to thiophenols were reduced from 410 nM, 365 nM to 62 nM, 33 nM respectively. Whereas, the good selectivity and short response time of probes 1a-b towards thiophenols was not affected in the presence of M-β-CD. Moreover, probes 1a-b were used for further water sample detection and HeLa cell imaging experiments due to their good response to thiophenols and the results suggested that probes 1a-b had the potential to detect the content of thiophenols in water samples and living cells.

Theoretical Investigation on the "ON-OFF" Mechanism of a Fluorescent Probe for Thiophenols: Photoinduced Electron Transfer and Intramolecular Charge Transfer

In this study, the sensing mechanism of (2E,4E)-5-(4-(dimethylamino)phenyl)-1-(2-(2,4dinitrophenoxy)phenyl)penta-2,4-dien-1-one (DAPH-DNP) towards thiophenols was investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT). The DNP group plays an important role in charge transfer excitation. Due to the typical donor-excited photo-induced electron transfer (d-PET) process, DAPH-DNP has fluorescence quenching behavior. After the thiolysis reaction between DAPH-DNP and thiophenol, the hydroxyl group is released, and DAPH is generated with the reaction showing strong fluorescence. The fluorescence enhancement of DAPH is not caused by an excited-state intramolecular proton transfer (ESIPT) process. The potential energy curves (PECs) show that DAPH-keto is less stable than DAPH-enol. The frontier molecular orbitals (FMOs) of DAPH show that the excitation process is accompanied by intramolecular charger transfer (ICT), and the corresponding character of DAPH was further confirmed by hole-electron and interfragment charge transfer (IFCT) analysis methods. Above all, the sensing mechanism of the turn-on type probe DAPH-DNP towards thiophenol is based on the PET mechanism.

Visual and quantitative monitoring of thiophenol by a novel deep-red emitting fluorescent probe in environmental and biological systems

Detection of highly toxic thiophenols in biological or environmental systems is of great importance. Therefore, fast, reliable, and sensitive probes are needed to detect thiophenols. Herein, a novel triphenylamine conjugated dicyanoisophorone-based near infrared fluorescence probe is reported to determine trace thiophenol (PhSH) levels. The probe demonstrates a distinct "turn-on" fluorescence response to thiophenol among the tested analytes and its quantum yield (Φ) increases from 0.011 to 0.142. It has low cytotoxicity with cell viability of 90-100% up to 10.0 μM of the probe, a strong anti-interference capability, a large Stokes shift (150 nm), and a fast response time (<1 min). In addition, the probe exhibits a good linear response to PhSH over the range from 0 to 15.0 μM with a detection limit of 32.3 nM (R² = 0.9978). The detection process is also confirmed through HPLC. The practical applicability of the probe is proved by a smartphone platform, TLC kit, plant tissue imaging, soil assay, tap, and lake water analysis with good recovery values (92.3-117%), and concentration-dependent live cell bioimaging PhSH from 5.0 to 15.0 μM. Therefore, the present probe is a robust candidate for monitoring PhSH levels in biological and environmental systems.

Highly porous gold supraparticles as surface-enhanced Raman spectroscopy (SERS) substrates for sensitive detection of environmental contaminants

Surface-enhanced Raman spectroscopy (SERS) has great potential as an analytical technique for environmental analyses. In this study, we fabricated highly porous gold (Au) supraparticles (i.e., ∼100 μm diameter agglomerates of primary nano-sized particles) and evaluated their applicability as SERS substrates for the sensitive detection of environmental contaminants. Facile supraparticle fabrication was achieved by evaporating a droplet containing an Au and polystyrene (PS) nanoparticle mixture on a superamphiphobic nanofilament substrate. Porous Au supraparticles were obtained through the removal of the PS phase by calcination at 500 °C. The porosity of the Au supraparticles was readily adjusted by varying the volumetric ratios of Au and PS nanoparticles. Six environmental contaminants (malachite green isothiocyanate, rhodamine B, benzenethiol, atrazine, adenine, and gene segment) were successfully adsorbed to the porous Au supraparticles, and their distinct SERS spectra were obtained. The observed linear dependence of the characteristic Raman peak intensity for each environmental contaminant on its aqueous concentration reveals the quantitative SERS detection capability by porous Au supraparticles. The limit of detection (LOD) for the six environmental contaminants ranged from ∼10 nM to ∼10 μM, which depends on analyte affinity to the porous Au supraparticles and analyte intrinsic Raman cross-sections. The porous Au supraparticles enabled multiplex SERS detection and maintained comparable SERS detection sensitivity in wastewater influent. Overall, we envision that the Au supraparticles can potentially serve as practical and sensitive SERS devices for environmental analysis applications.

A spectroscopic probe with FRET-ICT feature for thiophenol monitoring in real water samples

Thiophenol (PhSH) is widely used in industry, however, it is extremely harmful to the environment and human health due to its high toxicity. In this work, we developed a new FRET-ICT-based ratiometric fluorescent and colorimetric probe (DMNP) for detecting PhSH. DMNP had an ultrahigh energy transfer efficiency (99.7%) and clear spacing of two emission peaks (133 nm). DMNP achieved a fast response to PhSH and exhibited drastic enhancement (over 2100 folds) of the fluorescence intensity ratio upon addition of PhSH. DMNP showed good linear response in the PhSH concentration ranges of 0.5-13 μM and 17.0-22.0 μM. Meanwhile, DMNP could also be applied to monitor PhSH in a variety of real water samples.

The sensing mechanism of fluorescent probe for PhSH and the process of ESIPT

The detection mechanism of fluorescent probe FQ-DNP (DNP: 2,4-dinitropheno) for PhSH and the detailed ESIPT process of its product 2-(6-(diethylamino) quinolin-2-yl)-3-Hydroxy-4H-chromen-4-one (FQ-OH) have been revealed by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). For FQ-OH, the decreased bond length of H₆-N₇ and RDG analysis illustrate that the strength of hydrogen bond H₆-N₇ has been enlarged after photoexcitation, creating a good condition for ESIPT. To illustrate the ESIPT process in detail, the potential energy curves are performed and the transition state reaction energy is calculated. In the S₀ state, the FQ-OH could happen proton transfer (PT) to form keto, but the keto form is more unstable than enol form. After photoexcitation, in the S₁ state, FQ-OH could happen PT to produce stable keto form. Excited dynamic simulation shows that PT happens at 71.5 fs. The calculated absorption and emission spectra are in agreement with the experimental data, and the calculated Stokes shift is 160 nm. Frontier molecular orbitals (FMOs) and hole-electron analysis show that twisted intramolecular charge transfer (TICT) is responsible for the fluorescent quenching of FQ-DNP.

Double-site-based a smart fluorescent sensor for logical detecting of sulphides and its imaging evaluation of living organisms

Thiophenol and hydrosulphite are a group of toxic environmental pollutants, which contaminate land, water and food exhibiting a serious risk to human health. Herein, we reported a xanthene dye-based sensor (DSF) with dual well-known response sites for visual detecting PhSH and HSO₃^-. Specifically, when DSF reacted with PhSH firstly, the color of the solution changed to blue with bright red fluorescence emission. After added with HSO₃^-, the color of the solution became yellow, and emitted yellow fluorescence signal. However, DSF was first added with HSO₃^-, the color of the solution changed to purple with no-fluorescence emission, and then PhSH was added, the color of the solution changed to yellow with a bright yellow fluorescence. Notably, DSF exhibited high sensitivity and selectivity for PhSH and HSO₃^- detection with a very low detection limits of 2.27 nM and 22.91 nM, respectively. More importantly, DSF could detect PhSH and HSO₃^- in water, real-food and biological systems. Therefore, the experimental results showed DSF as a robust new logical monitoring tool for the detection of PhSH and HSO₃^- in water, real-food samples and biological systems.