Spectral imaging of chemical reactions using a computer display and a digital camera

Abstract

Various processes in chemistry lead to formation of spatial gradients, and cannot be directly studied using conventional spectroscopic techniques. Here we aimed to develop a simple method for the monitoring of light absorption at three wavelengths in two dimensions. The experimental setup consists of a commercial liquid crystal display (LCD) computer screen with light-emitting diode (LED) back illumination, and a digital camera equipped with a complementary metal oxide semiconductor imager. The computer screen serves as a multi-wavelength light source while the camera records distributions of the light transmitted through a two-dimensional non-homogeneous dynamic sample (reaction mixture). A program in C# language constantly changes the background colour of a console window, so as to alternately relay the light of different wavelength (λ_max = 608, 540, and 455 nm, respectively) onto the sample. The light emitted by the screen passes through a Petri dish containing the sample, while the digital camera records images revealing distributions of chemical substances absorbing at different wavelengths. The interval between two successive colour displays is 200–300 milliseconds. In this demonstration of the method, we followed two processes: the Belousov–Zhabotinsky oscillating reaction and the Old Nassau (Halloween) clock reaction. Every experiment produced a series of light absorption images corresponding to the wavelengths of the LCD/LED screen. Chemical front formation could be observed for analytes absorbing light at one of the three wavelength bands. In future, this approach can be extended to imaging at multiple wavelengths (by introducing customized LCD matrices and modified LED back illumination), and used in the monitoring of other non-homogeneous chemical processes.