Outer-Membrane Protease (OmpT) Based E. coli Sensing with Anionic Polythiophene and Unlabeled Peptide Substrate

Enzymes in Synergy: Bacteria Specific Molecular Probe for Locoregional Imaging of Urinary Tract Infection in vivo

Uropathogenic Escherichia coli (UPECs) is a leading cause for urinary tract infections (UTI), accounting for 70-90 % of community or hospital-acquired bacterial infections owing to high recurrence, imprecision in diagnosis and management, and increasing prevalence of antibiotic resistance. Current methods for clinical UPECs detection still rely on labor-intensive urine cultures that impede rapid and accurate diagnosis for timely UTI therapeutic management. Herein, we developed a first-in-class near-infrared (NIR) UPECs fluorescent probe (NO-AH) capable of specifically targeting UPECs through its collaborative response to bacterial enzymes, enabling locoregional imaging of UTIs both in vitro and in vivo. Our NO-AH probe incorporates a dual protease activatable moiety, which first reacts with OmpT, an endopeptidase abundantly present on the outer membrane of UPECs, releasing an intermediate amino acid residue conjugated with a NIR hemicyanine fluorophore. Such liberated fragment would be subsequently recognized by aminopeptidase (APN) within the periplasm of UPECs, activating localized fluorescence for precise imaging of UTIs in complex living environments. The peculiar specificity and selectivity of NO-AH, facilitated by the collaborative action of bacterial enzymes, features a timely and accurate identification of UPECs-infected UTIs, which could overcome misdiagnosis in conventional urine tests, thus opening new avenues towards reliable UTI diagnosis and personalized antimicrobial therapy management.

Correlating Molar Mass, π-Conjugation, and Optical Properties of Narrowly Distributed Anionic Polythiophenes in Aqueous Solutions

Polythiophene-based conjugated polyelectrolytes (CPE) are attracting increasing attention as sensor or interface materials in chemistry and biology. While cationic polythiophenes are better understood, limited structural information is available on their anionic counterparts. Limited access to well-defined polymers has made the study of structure-property relationships difficult and clear correlations have remained elusive. By combining controlled Kumada catalyst transfer polymerization with a polymer-analog substitution, regioregular and narrowly distributed poly(6-(thiophen-3-yl)hexane-1-sulfonate)s (PTHS) with tailored chain length are prepared. Analysis of their aqueous solution structures by small-angle neutron scattering (SANS) revealed a cylindrical conformation for all polymers tested, with a length close to the contour length of the polymer chains, while the estimated radii remain too small (<1.5 nm) for extensive π-stacking of the chains. The latter is particularly interesting as the longest polymer exhibits a concentration-independent structured absorption typical of crystalline polythiophenes. Increasing the ionic strength of the solution diminishes these features as the Coulomb repulsion between the charged repeat units is shielded, allowing the polymer to adopt a more coiled conformation. The extended π-conjugation, therefore, appears to be a key parameter for these unique optical features, which are not present in the corresponding cationic polythiophenes.

Wash-Free Amperometric Escherichia coli Detection via Rapid and Specific Proteolytic Cleavage by Its Outer Membrane OmpT

Various methods have been developed for the detection of Escherichia coli (E. coli); however, they are complex and time-consuming. OmpT─a cell membrane endopeptidase of E. coli─strongly embedded in the outer membrane of only E. coli, exposed to external solutions, with high proteolytic activity, could be a suitable target molecule for the rapid and straightforward detection of E. coli. Herein, a wash-free, sensitive, and selective amperometric method for E. coli detection, based on rapid and specific proteolytic cleavage by OmpT, has been reported. The method involved (i) rapid proteolytic cleavage of consecutive amino acids, after cleavage by OmpT, linked to an electrochemical species (4-aminophenol, AP), by leucine aminopeptidase (LAP, an exopeptidase), (ii) affinity binding of E. coli on an electrode, and (iii) electrochemical-enzymatic (EN) redox cycling. OmpT cleaved the intermediate peptide bond of a peptide substrate containing alanine-arginine-arginine-leucine-AP (-A-R-R-L-AP), forming R-L-AP, followed by the cleavage of two peptide bonds of R-L-AP sequentially by LAP, to liberate an electroactive AP. Affinity binding and EN redox cycling, in addition to rapid proteolytic cleavage by OmpT and LAP, enabled high electrochemical signal amplification. Two-sequential-cleavage was employed for the first time in protease-based detection. The calculated detection limit for E. coli cells in tap water (approximately 10³ CFU/mL after 1 h incubation) was lower than those obtained without affinity binding and EN redox cycling. The detection method was highly selective to E. coli as OmpT is present in only E. coli. High sensitivity, selectivity, and the absence of wash steps make the developed detection method practically promising.