The main advantage of optoacoustic imaging (OAI) is the capability to detect diseases at their early stages of growth. The efficiency of this technique has been demonstrated by preliminary studies with real biological tissues and small animals. The definitive goal of in-vivo OAI is to provide maps of the absolute concentration of chromophores with the help of exogenous optical contrast agents. Usually, solid-state lasers are used for the generation of ultrasounds but their use in clinical environment is inconvenient due to their large sizes, high costs, and low repetition rates (a few Hz) that are not sufficient for a high resolution during image processing. However, the requirements of high repetition rates (up a few kHz) can be fulfilled by high-power diode lasers (HPDLs) combined in side-by-side arrays. In the present paper, we implement a three-wavelength optoacoustic (OA) system consisting on a small array of HPDLs and a diode laser bar (DLB) operating at 870 nm, 905 nm, and 972 nm, respectively, coupled to a 1.2-mm diameter optical fiber bundle. The combined beam illuminates different mixtures of two gold nanorods solutions with absorbance peak at ~ 860 nm and ~ 900 nm, respectively, to generate OA signals. The pulses produced to generate OA signals are alternated between the three wavelengths by a microcontroller circuit with fast switching (0.33 ms). An inverse algorithm is implemented to estimate the concentrations of the nanoparticles solutions from the amplitude of the OA signals. The results achieved with our system show good agreement between the concentrations of gold nanorods estimated from measurements and the expected values.