Self-Immolative Polythiophene for Sunlight Inactivation of Harmful Cyanobacteria.

Harmful cyanobacterial blooms and the released microcystins (MCs) caused serious environmental and public health concerns to drinking water safety. Photo-oxidation is an appealing treatment option and alternative to conventional flocculation and microbial antagonists, but the performances of current photosensitizers (either inorganic or organic) are unsatisfactory. Here, a polythiophene photosensitizer (PT10) with both high yield of reactive oxygen species (ROS) production (mainly 1O2, ΦΔ = 0.51, > 8 h continuous generation) and moderate photostability was used as a powerful algaecide to inhibit Microcystis aeruginosa. Due to the positive charge of PT10, the algal cells were quickly flocculated, followed by efficient inactivation in 4 h under white light irradiation (96.7%, 10 mW/cm2). Meanwhile, PT10 was self-immolated in about 6 h. Upon biosafety evaluation with adult zebrafish, the low toxicity of PT10 and the degradation products of PT10 and algae (early logarithmic growth stage) were confirmed. In addition, microcystin-LR (MC-LR), a toxic microcystin that will be released during the destruction of the algal cells, was also degraded. Therefore, PT10-based photoinactivation of M. aeruginosa featured both high performance and low secondary pollution. In real-world aquatic systems, PT10 was confirmed to be capable of sunlight-assisted inactivation of M. aeruginosa and prevent algal blooms, thus making it appealing for environmental remediation.

Breaking the Photostability and pH Limitation of Halo-Fluoresceins through Chitosan Conjugation.

Halo-fluoresceins are widely used in cell and tissue staining, intracellular sensing, and photodynamic therapy, but their notorious photo-instability and pH dependence restrict their applications, especially in long-term visible light exposure and acidic environments. To overcome these limitations, here a strategy is proposed of conjugating chitosan with the carboxyl group of halo-fluorescein (CS-halofluorescein). The cross-linked polymer chains and the hydrogen-bonding networks of chitosan help shielding out 1 O2 from direct attacking the encapsulated halo-fluoresceins, leading to a two orders of magnitude lower photobleaching rate. Meanwhile, the condensation of primary amines of chitosan with the carboxyl group on halo-fluorescein blocks the pH-dependent intramolecular spirocyclization, leading to pH-inert fluorescein derivatives. The greatly improved photostability and pH inertness of CS-halofluoresceins can be harvested for aerobic photoredox synthesis and photodynamic bacteria inactivation in extremely acidic media. Moreover, food additive nature of chitosan and erythrosine (TIF) and excellent film-forming property of chitosan allow coating-based light-assisted preservation of perishable fruits, leading to appreciably extended shelf life of fruits (e.g., perishable strawberry, rt: > 3 days; 4 °C: > 5 days).

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.

Low-Cost Naked-Eye UVB and UVC Dosimetry Based on 3,3',5,5'-Tetramethylbenzidine.

Ultraviolet radiation (UVR) is both useful to human beings and can cause irreversible harm of varying degrees (UVA, UVB, and UVC). Especially, in areas with excessive sunlight, the appearance of UVB results in an increased risk of skin cancer. On the other hand, UV lamps (254 nm, UVC) are widely used in disinfection (air, water, and factory food) and hospital sterilization; the leakage of UVC is thus sometimes inevitable, which may cause fatal injuries to the related staff. Therefore, low-cost UV dosimetry-based personal protective equipment (PPE) and industrial monitoring devices are of great importance. Here, for the first time, we found that 3,3',5,5'-tetramethylbenzidine (TMB) could be rapidly oxidized upon UVB and UVC irradiation in a dose-dependent manner, in which TMB acts as a self-photosensitizer. Since TMB is a typical and widely used chromogenic substrate in enzyme-linked immunosorbent assay (ELISA), it is well-commercialized with low cost and vast availability worldwide, which permitted the development of low-cost naked-eye UVB and UVC dosimetry. A wearable bracelet mounted with TMB-loaded paper was developed for successful indication of whether the UVB exposure in the sunlight exceeded the minimum erythema dose (MED). In addition, we also developed a clock dial equipped with a TMB solution for unattended detection of UVC leakage from UVC disinfection lamps. The UVB- and UVC-selective coloration and low cost of TMB offered remarkable potential in facile detection of UVR in our daily life.

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.

Rationale of 3,3',5,5'-Tetramethylbenzidine as the Chromogenic Substrate in Colorimetric Analysis.

Horseradish peroxidase (HRP)-based assays feature particular interests because of the simple colorimetric readout. In these assays, 3,3',5,5'-tetramethylbenzidine (TMB) is the most widely used chromogenic substrates for HRP. The later research in nanozyme and DNAzyme also used TMB (the chosen substrate) because they are both HRP-mimics. It should be noted that the substrate of HRP is not just limited to TMB but, in fact, a broad range of benzidine derivatives. However, except decreased carcinogenicity due to tetrasubstitution of benzidine, the rationale for the chosen substrate TMB is not clear yet. Here, we addressed such a fundamental issue from the chemistry point of view. Nine benzidine derivatives featuring varied properties (different substitution groups and varied number of substitutions) were selected and investigated with four typical TMB-involved chromogenic systems. Among the existing benzidine substrates that are used for peroxidase-based assays, TMB exhibited the highest sensitivity, better color purity of colored products, and reasonable stability of oxidation products. Moreover, two tetrasubstituted benzidine derivatives other than TMB (4OCH3 and 2OCH32CH3) were synthesized for comparison. It turned out that the performances (sensitivity, color purity, and stability of the colored products) of TMB are still superior, thus chemically confirming its status of "the chosen substrate" in colorimetric assays.

Visualized detection of apo-transferrin based on cyanine dye supramolecular assembly.

In this work, a new biological probe for human transferrin (hTf) detection based on a cyanine dye ETC supramolecular assembly was designed. In sub-micromolar level, apo-hTf could induced the ETC aggregations transferred from H-aggregations to J-band with color change from pink to blue, while holo-hTf hardly possessed the ability, indicating ETC could specifically identify apo-hTf. The present study allowed for apo-hTf detection in the range of 8-80 nM with a detection limit of 2.8 nM and the sensitivity of visualization was around 70 nM. To further examine the suitability, iron ions were added into apo-hTf to stimulate the transformation from open conformation to the closed one gradually. It has been confirmed through tryptophan internal fluorescence quenching and the decrease of ETC J-aggregation. The interaction between ETC and apo-hTf performed high affinity that Ka was reached to 106 M-1 with a high selectivity. The potential in practical applications of this method has been tested for detection apo-hTf in human serum.

A Rapid Colorimetric Method to Visualize Protein Interactions.

As key molecules in most biological pathways, proteins physically contact one or more biomolecules in a highly specific manner. Several driving forces (i.e., electrostatic and hydrophobic) facilitate such interactions and a variety of methods have been developed to monitor these processes both in vivo and in vitro. In this work, a new method is reported for the detection of protein interactions by visualizing a color change of a cyanine compound, a supramolecule complex of 3,3-di-(3-sulfopropyl)-4,5,4',5'-dibenzo-9-methyl-thiacarbocyanine triethylammonium salt (MTC). Nuclear magnetic resonance (NMR) studies suggest that the hydrophobic nature of the protein surfaces drives MTC into different types of aggregates with distinct colors. When proteins interact with other biomolecules, the hydrophobic surface of the complex differs, resulting in a shift in the form of MTC aggregation, which results in a color change. As a result, this in vitro method has the potential to become a rapid tool for the confirmation of protein-biomolecule interactions, without the requirements for sophisticated instrumentation or approaches.