Surface Functionalised Optical Fibre for Detection of Hydrogen Sulphide.

Dysregulated production of hydrogen sulphide in the human body has been associated with various diseases including cancer, underlining the importance of accurate detection of this molecule. Here, we report the detection of hydrogen sulphide using fluorescence-emission enhancement of two 1,8-naphthalimide fluorescent probes with an azide moiety in position 4. One probe, serving as a control, featured a methoxyethyl moiety through the imide to evaluate its effectiveness for hydrogen sulphide detection, while the other probe was modified with (3-aminopropyl)triethoxysilane (APTES) to enable direct covalent attachment to an optical fibre tip. We coated the optical fibre tip relatively homogeneously with the APTES-azide fluorophore, as confirmed via x-ray photoelectron spectroscopy (XPS). The absorption and fluorescence responses of the control fluorophore free in PBS were analysed using UV-Vis and fluorescence spectrophotometry, while the fluorescence emission of the APTES-azide fluorophore-coated optical fibres was examined using a simple, low-cost optical fibre-based setup. Both fluorescent probes exhibited a significant increase (more than double the initial value) in fluorescence emission upon the addition of HS- when excited with 405 nm. However, the fluorescence enhancement of the coated optical fibres demonstrated a much faster response time of 2 min (time for the fluorescence intensity to reach 90% of its maximum value) compared to the control fluorophore in solution (30 min). Additionally, the temporal evolution of fluorescence intensity of the fluorophore coated on the optical fibre was studied at two pH values (7.4 and 6.4), demonstrating a reasonable overlap and confirming the compound pH insensitivity within this range. The promising results from this study indicate the potential for developing an optical fibre-based sensing system for HS- detection using the synthesised fluorophore, which could have significant applications in health monitoring and disease detection.

Development of an optical fiber-based redox monitoring system for tissue metabolism.

An optical redox ratio can potentially be used to report on the dynamics of cell and tissue metabolism and define altered metabolic conditions for different pathologies. While there are methods to measure the optical redox ratio, they are not particularly suited to real-time in situ or in vivo analysis. Here, we have developed a fiber-optic system to measure redox ratios in cells and tissues and two mathematical models to enable real-time, in vivo redox measurements. The optical redox ratios in tissue explants are correlated directly with endogenous NADH/FAD fluorescence emissions. We apply the mathematical models to the two-photon microscopy data and show consistent results. We also used our fiber-optic system to measure redox in different tissues and show consistent results between the two models, hence demonstrating proof-of-principle. This innovative redox monitoring system will have practical applications for defining different metabolic disease states.