Unraveling the Efficiency of Thioxanthone Based Triplet Sensitizers: A Detailed Theoretical Study

Photochemical activation by triplet photosensitizers is highly expedient for a green focus society. In this work, we have theoretically probed excited state characteristics of thioxanthone and its derivatives for their triplet harvesting efficiency using density functional theory (DFT) and time-dependent density functional theory (TDDFT). Absorption and triplet energies corroborate well with the available experimental data. Our results predict that both the S₁ and T₁ states are π-π^* in nature, which renders a high oscillator strength for S₀ to S₁ transition. Major triplet exciton conversion occurs through intersystem crossing (ISC) channel between the S₁ (¹π-π^*) and high energy ³n- π^* state. Apart from that, there is both radiative and non-radiative channel from S₁ to S₀, which competes with the ISC channel and reduces the triplet harvesting efficiency. For thioxanthones with −OMe (Me=Methyl) or −F substitution at 2 or 2’ positions, the ISC channel is not energetically feasible, causing sluggish intersystem crossing quantum yield (Φ_ISC). For unsubstituted thioxanthone and for isopropyl substitution at 2’ position, the S₁-T₁ gap is slightly positive ( ), rendering a lower triplet harvesting efficiency. For systems with −OMe or −F substitution at 3 or 3’ position of thioxanthone, because of buried π state and high energy π^* state, the S₁-³nπ^* gap becomes negative. This leads to a high Φ_ISC (>0.9), which is key to being an effective photocatalyst.     

A Novel Electroanalytical Biosensor Based on ZIF-8/Acetylcholinesterase Bio-nanohybrids for Early Management of Hirschsprung Disease

Hirschsprung's disease (HD) is characterised by missing nerve cells in the colon of infants and children which results in strained bowel movement. Under such situations, undiagnosed and untreated cases often lead to a cascade of gastrointestinal infections eventually resulting in Hirschsprung-assisted enterocolitis which has significantly high mortality rate. This is further exacerbated by the absence of suitable, sensitive and efficient technologies to detect the pathological segment of the intestine, which could significantly reduce surgery duration in the operation theatre, as well as associated risks to patients. It therefore becomes a matter of extreme importance to develop a point-of-care platform for early and efficient management/identification of the occurrence of HD in neonates and older children during its onset, before it proves fatal with life-threatening outcomes. The present work reports an electrochemical enzymatic biosensor using Zeolitic Imidazolate Framework-8 (ZIF-8) modified with acetylcholinesterase enzyme (AchE), for detection of HD as a function of the key biomarker – acetylcholine. The developed sensor was initially characterized using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS), while the analytical performance and insights onto interfacial redox kinetics were assessed using Differential Pulse Voltammetry (DPV) and EIS respectively. The sensor exhibited limit of detection and sensitivity of 0.19 μM and sensitivity of 0.42 μA/μM/mm² with a shelf life of 1 month, while remaining unperturbed in the presence of common interferants. The performance of developed sensor was also examined in spiked serum samples and was observed to yield a high degree of linearity.