Pulse oximetry is one of the most commonly employed monitoring modalities in critical care setting. Conventional pulse oximeters use two leds at different wavelengths and a photodiode to estimate blood oxygen saturation noninvasively, based in the difference of absorption coefficients between hemoglobin and deoxyhemoglobin. Nevertheless, factors such as low oxygen saturations or led wavelength displacement, modify differently the expected light absorbance for both LEDs. To address this issue, we propose a novel approach combining a single led and a Buried Quad Junction photodetector, i.e. a multispectral sensor. With this fundamental modification of the pulse oximetry principle, we reduce the modifying effects introduced by the aforementioned sources of inaccuracy by using a single led. Results from in vivo measurements, show that two of the three tests of the proposed system's precision falls within the commercial tolerance of 34% SpO2%