Laser-fabricated superhydrophobic/superhydrophilic surfaces on silicon wafer for terahertz spectroscopic detection of aqueous solutions

Terahertz (THz) spectroscopic detection technology is regarded as an ideal approach for detecting biological substances due to its unique advantages of non-ionization, high penetrability, and fingerprint spectra. However, because of the strong absorption of THz waves by polar molecules, such as water, detecting target substances dissolved in water is challenging. We propose a new method of tuning the thickness of an aqueous solution film using a superhydrophobic/superhydrophilic (SHB/SHL) surface to improve the ability to obtain the THz spectral information of hydrated substances. The SHB/SHL surface is fabricated on a silicon wafer by regulating cross-grooved micro-/nano-structures with laser texturing. Droplets of the solution can be fixed in a controlled way in a region on the SHB/SHL surface, and then the thickness of the liquid film can be adjusted to optimize the THz transmission signal. This method for detecting target substances dissolved in water focuses more on the coordination between the thickness of the aqueous solution and the THz intensity than the radiation energy. Furthermore, we detect a-lactose in solutions through different thicknesses of the film, which shows the method to be effective for dilute solutions.