Light-activated, dual-mode fluorescence and colorimetric detection of estradiol with high fidelity based on aptamer's special recognition

The intake of estradiol residue from food will lead to health problems, so the rapid and reliable detection of estradiol residue is essential. Multi-mode assays are inherently self-correcting and self-validating, providing more reliable, interference-resistant, high-fidelity results. Here, we developed a dual-mode method to achieve a rapid, reliable, and sensitive detection of estradiol. The binding of thioflavin T to the cavity sites of estradiol aptamer not only generates a strong fluorescence signal, but also provides light-activated oxidase activity to produce a blue oxidation product. But the specific binding between aptamer and estradiol will compete with the above process. Thus a dual-mode fluorescence and colorimetric detection of estradiol was realized with a detection limit of 0.15 μM or 0.27 μM. Besides, the dual-mode method showed a good selectivity for estradiol detection. The method could detect estradiol in meat food, showing a good application potential to monitor endocrine-disrupting chemical.

Sensitive acid phosphatase assay based on light-activated specific oxidase mimic activity

Acid phosphatase (ACP) is a key marker in the diagnosis of many diseases. However, exploiting a simple and sensitive sensor for the real-time quantitative analysis of ACP is still challenging. Herein, we attempted to develop a sensitive colorimetric sensing strategy for the detection of ACP based on light-activated oxidase mimic property of carbon dots (CDs). The synthesized CDs were proved to be capable of intrinsic light-activated oxidase mimic activity, which could generate reactive oxygen species to oxidize chromogenic substrate under ultraviolet light stimulation. Interestingly, this light-activated oxidase mimic behavior would be effectively suppressed by the antioxidant ascorbic acid (AA), a product from the hydrolysis of 2-phospho-L-ascorbic acid trisodium (AAP) mediated by ACP. Based on the above property, a facile and sensitive colorimetric sensing method for ACP was developed. Under the optimal conditions, the linear range for ACP 0.1-5.5 U/L, and the detection limit was 0.056 U/L. Compared with conventional nanozyme based ACP assay systems, the catalytic activity of light-activated nanozyme could be conveniently regulated by switching the light on and off, which made it easier to precisely control the extent of the reaction and ensured the accuracy of the assay. In addition, the proposed sensing system would be readout directly by the naked eye or smartphone-based RGB analysis system, and have been successfully applied to analyze diluted in diluted fetal bovine serum and urine samples spiked with ACP. All these results indicated that this approach holds good promise for future applications in clinical analysis and point-of-care (POC) biosensor platforms.

Photoactivated 2,3-distyrylindoles kill multi-drug resistant bacteria

Compounds based on the 2,3-distyrylindole scaffold were found to exhibit bactericidal properties upon irradiation with white light. At the concentration of 1 μM, the lead compound 1 completely (ca. 109 CFU/mL) eradicated such Gram-positive organisms as S. aureus (MRSA, MSSA), E. faecalis (VRE), S. pyogenes and S. mutans when irradiated with white light for 2 min. At the concentration of 5 μM and in the presence of polymyxin E at non-bactericidal 1.25 μg/mL concentration, 1 also showed a 7-log to 9-log reductions in bacterial counts of such Gram-negative organisms as multi-drug resistant (MDR) A. baumannii, MDR P. aeruginosa, E. coli and Klebsiella pneumoniae (CRE: KPC and NDM-1), also when irradiated with white light for 2 min. The structure-activity relationship studies revealed that unsubstituted at benzene rings 2,3-distyrylindole 2 was most potent and gave a 5-order of magnitude eradication of a MRSA strain at the concentration of 30 nM upon irradiation with white light. Initial mechanistic experiments revealed the disruption of bacterial cell membrane, but indicated that singlet oxygen production, which is commonly associated with photodynamic therapy, may not play a role in the bactericidal effects of the 2,3-distyrylindoles.

Ruthenium dihydroxybipyridine complexes are tumor activated prodrugs due to low pH and blue light induced ligand release

Ruthenium drugs are potent anti-cancer agents, but inducing drug selectivity and enhancing their modest activity remain challenging. Slow Ru ligand loss limits the formation of free sites and subsequent binding to DNA base pairs. Herein, we designed a ligand that rapidly dissociates upon irradiation at low pH. Activation at low pH can lead to cancer selectivity, since many cancer cells have higher metabolism (and thus lower pH) than non-cancerous cells. We have used the pH sensitive ligand, 6,6'-dihydroxy-2,2'-bipyridine (66'bpy(OH)2), to generate [Ru(bpy)2(66'(bpy(OH)2)](2+), which contains two acidic hydroxyl groups with pKa1=5.26 and pKa2=7.27. Irradiation when protonated leads to photo-dissociation of the 66'bpy(OH)2 ligand. An in-depth study of the structural and electronic properties of the complex was carried out using X-ray crystallography, electrochemistry, UV/visible spectroscopy, and computational techniques. Notably, RuN bond lengths in the 66'bpy(OH)2 complex are longer (by ~0.3Å) than in polypyridyl complexes that lack 6 and 6' substitution. Thus, the longer bond length predisposes the complex for photo-dissociation and leads to the anti-cancer activity. When the complex is deprotonated, the 66'bpy(O(-))2 ligand molecular orbitals mix heavily with the ruthenium orbitals, making new mixed metal-ligand orbitals that lead to a higher bond order. We investigated the anti-cancer activities of [Ru(bpy)2(66'(bpy(OH)2)](2+), [Ru(bpy)2(44'(bpy(OH)2)](2+), and [Ru(bpy)3](2+) (44'(bpy(OH)2=4,4'-dihydroxy-2,2'-bipyridine) in HeLa cells, which have a relatively low pH. It is found that [Ru(bpy)2(66'(bpy(OH)2)](2+) is more cytotoxic than the other ruthenium complexes studied. Thus, we have identified a pH sensitive ruthenium scaffold that can be exploited for photo-induced anti-cancer activity.