Search

Development of rapid detection strategies that target potentially pathogenic bacteria has gained increasing attention due to the increasing awareness for better health and safety. In this study, we evaluate an intrinsically antimicrobial polymer, 2Gdm, which is a poly(norbornene)-based functional polymer featuring guanidinium groups as side chains, for bacterial detection by the means of triboelectric nanogenerators (TENGs) and triboelectric nanosensors (TENSs). Attachment of bacteria to the sensing layer is anticipated to alter the overall triboelectric properties of the underlying polymer layer. The positively charged guanidinium functional groups can interact with the negatively charged phospholipid bilayer of bacteria and lead to bacterial death, which can then be detected by optical microscopy, X-ray photoelectron microscopy, and more advanced self-powered sensing techniques such as TENGs and TENSs. The double bonds present along the poly(norbornene) backbone allow for thermally induced cross-linking to obtain X-2Gdm and thus rendering materials remain stable in water. By monitoring the change in voltage output after immersion in various concentrations of Gram-negative Escherichia coli(E. coli) and Gram-positive Streptococcus pneumoniae(S. pneumoniae), we have demonstrated the utility of X-2Gdm as a new polymer dielectric for autonomous bacterial detection. As the bacterial concentration increases, the amount of adsorbed bacteria also increases, resulting in a decrease in the surface potential of the X-2Gdm thin film; this reduction in surface potential can cause a decrease in the triboelectric output for both TENGs and TENSs, which serves as a key working mechanism for facile bacterial detection. TENG and TENS systems are capable of detecting E. coliand S. pneumoniaewithin a range of 4 × 105to 4 × 108CFU/mL with a limit of detection of 106CFU/mL. This report highlights the promising prospects of employing TENGs and TENSs as innovative sensing technologies for rapid bacterial detection by leveraging the electrostatic interactions between bacterial cell membranes and cationic groups present on polymer surfaces.

The novel multistimuli-responsive monofluorophoric supramolecular polymer Poly(TPE-DBC)/FL-DBAand pseudo[3]rotaxane TPE-DBC/FL-DBAconsisted of the closed form of nonemissive fluorescein guest FL-DBAalong with TPE-based main-chain macrocyclic polymer Poly(TPE-DBC)and TPE-functionalized macrocycle TPE-DBChosts, respectively. By the combination of various external stimuli, these fluorescent supramolecular host–guest systems could reveal interesting photoluminescence (PL) properties in DMF/H2O (1:1, v/v) solutions, including bifluorophoric host–guest systems after the complexation of Al3+ion, i.e., TPE-DBC/FL-DBA-Al3+and Poly(TPE-DBC)/FL-DBA-Al3+with their corresponding open form of fluorescein guest FL-DBA-Al3+. Importantly, the Förster resonance energy transfer (FRET) processes occurred in both bifluorophoric host–guest systems between blue-emissive TPE donors (λem= 470 nm) and green-emissive fluorescein acceptors (λem= 527 nm) after aluminum detection, which were further verified by time-resolved photoluminescence (TRPL) measurements to acquire their FRET efficiencies of 40.4 and 31.1%, respectively. Both supramolecular host–guest systems exhibited stronger green fluorescein emissions as well as appealing ratiometric PL behaviors within the desirable donor–acceptor distances of FRET processes in comparison with their detached analogous mixtures. Regarding the pH effects, the optimum green fluorescein emissions with effective FRET processes of all compounds and host–guest systems were sustained in the range pH = 7–10. Interestingly, both host–guest systems TPE-DBC/FL-DBAand Poly(TPE-DBC)/FL-DBApossessed high sensitivities and selectivities toward aluminum ion to display their strong green emissions via FRET-ON behaviors due to the chelation-induced ring opening of spirolactam moieties to become green-emissive guest acceptor FL-DBA-Al3+, which offered excellent limit of detection (LOD) values of 50.61 and 38.59 nM, respectively, to be further applied for the fabrication of facile test strips toward aluminum detection. Accordingly, the inventive ratiometric PL and FRET sensor approaches of supramolecular host–guest systems toward aluminum ion with prominent sensitivities and selectivities were well-established in this study.

A supramolecular [2]pseudo-rotaxane containing a naphthalimide-based pillararene host and a spiropyran-based imidazole guest was synthesized and investigated in a semiaqueous solution with 90% water fraction. Upon UV exposure, the close-form structure of nonemissive spiropyran guest could be transformed into the open-form structure of red-emissive merocyanine guest reversibly, which was utilized as a monofluorophoric sensor to detect copper(II) and cyanide ions. Moreover, the naphthalimide host as an energy donor with green photoluminescence (PL) emission at 505 nm was complexed with the merocyanine guest as an energy acceptor with red PL emission at 650 nm in 1:1 molar ratio to generate a [2]pseudo-rotaxane polymer, which was further verified by the diffusion coefficients of DOSY nuclear magnetic resonance (NMR) measurements. Due to the Förster resonance energy transfer (FRET) processes, the bifluorophoric [2]pseudo-rotaxane produced more efficient ratiometric PL behavior to induce a stronger red PL emission than that of the monofluorophoric guest; therefore, the PL sensor responses of the supramolecular [2]pseudo-rotaxane toward copper(II) and cyanide ions could be further amplified via the FRET-OFF processes to turn off red PL emission of the reacted merocyanine acceptor and to recover green PL emission of the naphthalimide donor. Accordingly, the best and prominent values of the limit of detection (LOD) for the host–guest detections toward Cu2+and CN–were 0.53 and 1.34 μM, respectively. The highest red MC emission with the optimum FRET processes of [2]pseudo-rotaxane was maintained around room temperature (20–40 °C) in wide pH conditions (pH = 3–13), which can be utilized in the cell viability tests to prove the nontoxic and remarkable biomarker of [2]pseudo-rotaxane to detect Cu2+and CN–in living cells. The developed FRET-OFF processes with ratiometric PL behavior of the bifluorophoric supramolecular [2]pseudo-rotaxane polymer will open a new avenue to the future applications of chemo- and biosensors.

A series of multistimuli-responsive [2]rotaxanes with a naphthalimide-functionalized macrocycle threaded through an axle containing a photochromic spiropyran (SP) or merocyanine (MC) stopper were fabricated and studied for their distinct photophysical properties in semiaqueous solutions. By different combinations of chemical and photochemical switchable stimuli, these [2]rotaxanes could be interconverted between multiple states, including monofluorophoric [2]rotaxanes with the close form of the SP unit, i.e., Rot-H-SPand Rot-SPbefore and after shuttling upon acid–base controls, respectively, along with their corresponding bifluorophoric [2]rotaxanes possessing the open form of the MC unit, i.e., Rot-H-MCand Rot-MCafter UV exposure. Interestingly, the photoinduced electron-transfer (PET) effects appeared between nonemissive SP and aggregation-caused quenching (ACQ) naphthalimide units in [2]rotaxanes Rot-H-SPand Rot-SP, whereas the Förster resonance energy transfer (FRET)/Dexter energy transfer occurred in [2]rotaxanes Rot-H-MCand Rot-MCbetween green-emissive naphthalimide donor (λem= 528 nm) and red-emissive MC acceptor (λem= 648 nm) moieties after UV exposure. Moreover, the PET as well as FRET/Dexter energy-transfer processes and the speculated molecular arrangements (with/without macrocyclic tilting) of all [2]rotaxanes and related derivatives were verified by time-resolved photoluminescence (TRPL) measurements and theoretical studies. Among all [2]rotaxanes and derivatives, Rot-MCin tetrahydrofuran (THF)/H2O (2:8, v/v) revealed the strongest red MC emission with the most effective FRET process that possessed attractive ratiometric photoluminescence (PL) due to the ideal shortest donor–acceptor distance. Regardless of pH and temperature effects, the highest red MC emissions with the optimum FRET processes of all compounds were maintained at room temperature in near-neutral conditions (i.e., pH = 5–9). Importantly, the red-emissive [2]rotaxane Rot-MCshowed high selectivity and sensitivity toward sulfite-ion sensing to recover green donor emission via FRET-OFF behavior owing to the Michael reaction of the MC moiety with the sulfite ion, which had an excellent limit of detection (LOD) value of 0.76 μM to be further utilized for the cellular imaging of sulfite detection in living cells. Accordingly, the novel ratiometric sensor approaches of bifluorophoric [2]rotaxane systems have been well developed in this study as the first rotaxane application of FRET processes toward sulfite detection with higher sensitivities than those of their monofluorophoric analogues. Various LOD values could be evaluated to realize the sulfite-sensing mechanisms of well-designed [2]rotaxane systems by the shuttling of macrocyclic fluorophores along with photoswitchable FRET behaviors via alternative UV–vis exposures.

Ozonolysis of isoprene to produce Criegee intermediates such as methyl vinyl ketone oxide (MVKO), C2H3C(CH3)OO, is an important process in atmospheric chemistry. MVKO was recently produced and identified in laboratories after photolysis of a gaseous mixture of 1,3-diiodo-but-2-ene, (CH2I)HC═C(CH3)I, and O2, but the mechanism of its formation remains unexplored. We synthesized pure (Z)- and (E)-1,3-diiodo-but-2-ene and measured their distinct IR spectra. Upon irradiation at 280 nm of (Z)- and (E)-1,3-diiodo-but-2-ene in solid p-H2at 3.3 K, the fission of the terminal C—I bond yields (Z)- and (E)-3-iodo-but-2-en-1-yl [•C2H3C(CH3)I] radicals, respectively. These radicals were characterized with infrared absorption lines at 2962.4, 1423.8, 1265.3, 1120.9/1127.0, 921.4/922.3, and 792.5/791.7 cm–1, and 16 additional weaker lines for (Z)-•C2H3C(CH3)I and 1405.2, 1208.2, 1106.0/1103.9, 934.2/933.4, and 785.1/784.9 cm–1and five additional weaker ones for (E)-•C2H3C(CH3)I. The assignments were derived according to behavior on secondary photolysis and comparison of the vibrational wavenumbers and the IR intensities of observed lines with those calculated with the B2PLYP-D3/aug-cc-pVTZ-pp method. These observations confirmed that only the terminal I atom, not the central one, was photodissociated at 280 nm and, in solid p-H2, the excess energy after photodissociation induced no change in conformation. These new spectra of •C2H3C(CH3)I radicals can provide valuable information for the understanding of the mechanism of formation of Criegee intermediate MVKO from the source reaction of photolysis of (CH2I)HC═C(CH3)I in O2in the laboratory.

Bistable [c2] daisy chain rotaxanes with respective extended and contracted forms of [c2]Aand [c2]Bcontaining a blue-emissive anthracene (AN) donor and orange-emissive indandione-carbazole (IC) acceptor were successfully synthesized via click reaction. Tunable-emission bistable [c2] daisy chain rotaxanes with fluorescence changes from blue to orange, including bright-white-light emissions, could be modulated by the aggregation-induced emission (AIE) characteristics and Förster resonance energy transfer (FRET) processes through altering water fractions and shuttling processes (i.e., acid/base controls). Accordingly, as a result of excellent fine-tuning AIE (at 60% water content of H2O/THF) and FRET (with a compatible energy transfer of EFRET= 33.2%) behaviors after the shuttling process (by adding base), the brightest white-light emission at CIE (0.31, 0.37) with a quantum yield of Φ = 15.64% was obtained in contracted [c2]Bwith good control of molecular shuttling to possess higher photoluminescence (PL) quantum yields and better energy transfer efficiencies (i.e., the manipulation of reduced PET and enhanced FRET processes) due to their intramolecular aggregations of blue ANdonors and orange ICacceptors with a proper water content of 60% H2O. Furthermore, dynamic light-scattering (DLS) and time-resolved photoluminescence (TRPL) measurements, along with theoretical calculations, were utilized to investigate and confirm AIE and FRET phenomena of bistable [c2] daisy chain rotaxanes. Especially, both bistable [c2] daisy chain rotaxanes [c2]Aand [c2]Band noninterlocked monomer Mcould be exploited for the applications of ratiometric fluorescence temperature sensing due to the temperature effects on the AIE and FRET features. Based on these desirable bistable [c2] daisy chain rotaxane structures, this work provides a potential strategy for the future applications of tunable multicolor emission and ratiometric fluorescence temperature-sensing materials.

Fluorescent silicon quantum dots (SiQDs) have shown a great potential as antiphotobleaching, nontoxic and biodegradable labels for various in vitro and in vivo applications. However, fabricating SiQDs with high water-solubility and high photoluminescence quantum yield (PLQY) remains a challenge. Furthermore, for targeted imaging, their surface chemistry has to be capable of conjugating to antibodies, as well as sufficiently antifouling. Herein, antibody-conjugated SiQD nanoparticles (SiQD-NPs) with antifouling coatings composed of bovine serum albumin (BSA) and polyethylene glycol (PEG) are demonstrated for immunostaining on live cancer cells. The monodisperse SiQD-NPs of diameter about 130 nm are synthesized by a novel top-down method, including electrochemical etching, photochemical hydrosilylation, high energy ball milling, and “selective-etching” in HNO3and HF. Subsequently, the BSA and PEG are covalently grafted on to the SiQD-NP surface through presynthesized chemical linkers, resulting in a stable, hydrophilic, and antifouling organic capping layer with isothiocyanates as the terminal functional groups for facile conjugation to the antibodies. The in vitro cell viability assay reveals that the BSA-coated SiQD-NPs had exceptional biocompatibility, with minimal cytotoxicity at concentration up to 1600 μg mL–1. Under 365 nm excitation, the SiQD-NP colloid emits bright reddish photoluminescence with PLQY = 45–55% in organic solvent and 5–10% in aqueous buffer. Finally, through confocal fluorescent imaging and flow cytometry analysis, the anti-HER2 conjugated SiQD-NPs show obvious specific binding to the HER2-overexpressing SKOV3 cells and negligible nonspecific binding to the HER2-nonexpressing CHO cells. Under similar experimental conditions, the immunofluorescence results obtained with the SiQD-NPs are comparable to those using conventional fluorescein isothiocyanate (FITC).

An isolated yeast strain was grown aerobically on phenol as a sole carbon source up to 24 mM; the rate of degradation of phenol at 30 °C was greater than other microorganisms at the comparable phenol concentrations. This microorganism was further identified and is designated Candida albicansTL3. The catabolic activity of C. albicansTL3 for degradation of phenol was evaluated with the Ksand Vmaxvalues of 1.7±0.1 mMand 0.66±0.02 μmol/min/mg of protein, respectively. With application of enzymatic, chromatographic and mass-spectrometric analyses, we confirmed that catechol and cis,cis-muconic acid were produced during the biodegradation of phenol performed by C. albicansTL3, indicating the occurrence of an ortho-fission pathway. The maximum activity of phenol hydroxylase and catechol-1,2-dioxygenase were induced when this strain grew in phenol culture media at 22 mMand 10 mM, respectively. In addition to phenol, C. albicansTL3 was effective in degrading formaldehyde, which is another major pollutant in waste water from a factory producing phenolic resin. The promising result from the bio-treatment of such factory effluent makes Candida albicansTL3 be a potentially useful strain for industrial application.

β-Glucosidase from Flavobacterium meningosepticum (Fbgl) catalyses the hydrolysis of β-1,4-glucosidic bonds via a two-step double-displacement mechanism in which two amino acid residues act as nucleophile and acid/base catalyst. Definitive identification of these two residues is provided by the two active-site-directed inactivators, 2′,4′-dinitrophenyl-2-deoxy-2-fluoro-β-d-glucoside (2FDNPG) and N-bromoacetyl-β-d-glucosylamine (NBGN), which stoichiometrically label the nucleophile and the acid/base catalyst of Fbgl, respectively. Pseudo-first-order inactivation rate constants (ki) of 0.25±0.01 and 0.05±0.01min−1 and dissociation constants (Ki) of 90±15 and 4.4±0.2mM are determined for 2FDNPG and NBGN, respectively. Proteolytic digestion of the labelled proteins, followed by peptide mapping and tandem MS analysis identify Asp-247 and Glu-473 as the catalytic nucleophile and acid/base residues, respectively, of Fbgl. This study confirms that the catalytic nucleophile of family 3 glycohydrolase is conserved across sub-families. However, different sub-families may have unique general acid/base catalysts.

A family 3 β-glucosidase (EC 3.2.1.21) from Flavobacterium meningosepticum has been cloned and overexpressed. The mechanistic action of the enzyme was probed by NMR spectroscopy and kinetic investigations, including substrate reactivity, secondary kinetic isotope effects and inhibition studies. The stereochemistry of enzymic hydrolysis was identified as occurring with the retention of an anomeric configuration, indicating a double-displacement reaction. Based on the kcat values with a series of aryl glucosides, a Bronsted plot with a concave-downward shape was constructed. This biphasic behaviour is consistent with a two-step mechanism involving the formation and breakdown of a glucosyl–enzyme intermediate. The large Bronsted constant (β =-0.85) for the leaving-group-dependent portion (pKa of leaving phenols > 7) indicates substantial bond cleavage at the transition state. Secondary deuterium kinetic isotope effects with 2,4-dinitrophenyl β-D-glucopyanoside, o-nitrophenyl β-D-glucopyanoside and p-cyanophenyl β-D-glucopyanoside as substrates were 1.17±0.02, 1.19±0.02 and 1.04±0.02 respectively. These results support an SN1-like mechanism for the deglucosylation step and an SN2-like mechanism for the glucosylation step. Site-directed mutagenesis was also performed to study essential amino acid residues. The activities (kcat/Km) of the D247G and D247N mutants were 30000- and 200000-fold lower respectively than that of the wild-type enzyme, whereas the D247E mutant retained 20% of wild-type activity. These results indicate that Asp-247 is an essential amino acid. It is likely that this residue functions as a nucleophile in the reaction. This conclusion is supported by the kinetics of the irreversible inactivation of the wild-type enzyme by conduritol-B-epoxide, compared with the much slower inhibition of the D247E mutant and the lack of irreversible inhibition of the D247G mutant.