Surface refractive index sensor based on titanium dioxide composite thin film for detection of cadmium ions

•A green TiO2-based nanocomposite thin film was developed.•The sensing potential of developed thin film against different concentration of cadmium ions was investigated.•The changes of refractive index and thickness upon the interaction of cadmium ions were theoretically confirmed.•The minimum detectable concentration of Cd ions was 10 ppb. In this work, a refractive index sensor using TiO2 extracted from moringa leaves-based nanocomposite thin film was developed to detect cadmium ions in an aqueous solution. The experimental results showed a good sensitivity response of 0.4825° ppm−1, a strong binding affinity of 1.4362 ppm−1, and a low signal-to-noise ratio of 0.0755. The proposed sensor also showed good selectivity towards cadmium ions compared to zinc and mercury ions. The changes in the optical properties of titanium dioxide-based nanocomposite thin film towards different concentrations of cadmium ions solution were further demonstrated theoretically. Also, the observed increase in the surface roughness using atomic force microscopy proved the binding of Cd ions to the sensor film. This study is proposing a new potential of titanium dioxide extracted from moringa leaves-based nanocomposite thin film as a surface refractive index sensor for the detection of cadmium ions.