Analysis of the Isotopic Purity of D2O with the Characteristic NIR-II Phosphorescence of Singlet Oxygen from a Photostable Polythiophene Photosensitizer.

D2O plays important roles in a variety of fields (such as the nuclear industry and bioorganic analysis), and thus its isotopic purity (H2O contents) is highly concerned. Due to its highly similar physical properties to H2O and large excess amounts of H2O over D2O, it is challenging to distinguish D2O from H2O. On the basis of the characteristic NIR-II phosphorescence of singlet oxygen (1O2), and the fact that H2O is a more efficient quencher for 1O2 than D2O, here, we proposed to simply use the 1275 nm emission of 1O2 for the analysis of the isotopic purity of D2O. In normal cases (a xenon lamp for excitation), such steady-state emission is extremely weak for valid analytical applications, we thus employed laser excitation for intensification. To this goal, a series of photosensitizers were screened, and eventually polythiophene PT10 was selected with high singlet oxygen quantum yield (ΦΔ = 0.51), high H2O/D2O contrast, and excellent photostability. Upon excitation with a 445 nm laser, a limit of detection (LOD, 3σ) of 0.1% for H2O in D2O was achieved. The accuracy of the proposed method was verified by the analysis of the isotopic purity of several D2O samples (with randomly added H2O). More interestingly, the hygroscopicity of D2O was sensitively monitored with the proposed probe in a real-time manner; the results of which are important for strengthening the care of D2O storage and the importance of humidity control during related investigations. Besides D2O isotopic purity evaluation, this work also indicated the potential usefulness of the NIR-II emission of singlet oxygen in future analytical detection.

Polythiophene as a near full pH photo-antimicrobial.

Microbial infections are currently one of the world's major public health concerns, the evolution of which has resulted in the development of multiple tolerances (not just drug or antibiotic resistance), including pH (from extremely acidic to alkaline). Currently various types of antimicrobials have been developed. Although effective, they seldom work in the full pH range due to the existence of acid-/base-reaction sites. Here, we found that polythiophene (PT10), a cationic polymer, was capable of both broad-spectrum photo-antimicrobial activity (Gram positive, Gram negative, Fungal, and cyano-bacteria) and broad pH responsiveness (constant 1O2 generation at pH 2-13). The half-maximal inhibitory concentrations (IC50) of PT10 for bacteria living in acidic, neutral, and alkaline media were generally lower than 2 µg mL-1 (except M. aeruginosa, pH 12, ∼30 µg mL-1), which were much lower than common antibiotics and other photosensitizers. Besides, the excellent photostability of PT10 allowed long-term light irradiation for antimicrobial performance. In real-world applications, PT10 was explored for the successful in vivo therapy of oral Candidiasis infection under extreme acidic conditions (pH < 3) and the removal of M. aeruginosa at pH 12. Such near full pH, broad-spectrum photo-antimicrobial activity of polythiophene is appealing for extremely acidic or alkaline applications, such as oral infections, vaginitis, and blooms.