Detecting fluorescence in molecular rotors due to shear stress in a flow chamber [abstract]

Abstract

Molecular rotors are molecules that have two methods of deexcitation: intramolecular rotation or fluorescence emission. It has recently been established that some rotors increase emission intensity in sheared fluids (Haidekker MA et al, Sensor Letters. 2005; 3: 42-8), which gives rise to a new concept of high sensitivity, real-time and microscale flow and shear sensors. The purpose of this study was to observe fluorescence intensity patterns related to fluid shear stress in flow chambers of various geometries. 40µl of a molecular rotor, 9-(2-carboxy-2-cyano)-vinyl-julolidine (CCVJ), was dissolved in two fluids of different viscosities: 40ml of ethylene glycol (EG) or a mixture of 20ml water and 5ml of EG. Using a syringe pump, flow rates of 0ml/min, 0.25ml/min, 0.50ml/min, 0.75ml/min, 1.0ml/min, and 1.5ml/min were used for EG and flow rates of 0ml/min, 3ml/min, 4ml/min, 5ml/min, 6ml/min, and 7ml/min for water with EG. Unsupervised image processing was used to denoise, scale the images, and compute the relative difference of intensity at flow (IF) to intensity at rest (IR) using I = (IF-IR)/IR. The intensity difference was up to 10% higher in sections of the flow chamber with high flow rate. In fact, areas where high fluid shear stress could be expected correlated well with areas of high relative intensity. It was also observed that the intensity was not always homogeneous in areas where homogeneous flow within the flow chamber would be expected. This may be attributed to imperfections of the flow channel. A further step, flow simulation with computed fluid dynamics (CFD), is needed to quantitatively correlate intensity to flow velocity and shear stress. This new fluorescent method provides highly sensitive real time observations of flow patterns in situ.