We report on a photothermal modulation detection scheme developed using a swept source-based optical coherence tomography (OCT) system centred at 1300nm. Photothermal detection is an improved technique for studying the contrast properties of exogenous contrast agents such as highly absorbing polypyrrole (PPy) nanoparticles used for OCT imaging. The swept source based OCT system has a wavelength sweep rate of 10 kHz which is used for the phase modulation detection of various concentrations of PPy nanoparticles. PPy nanoparticles have been recently reported to be a promising candidate for OCT imaging owing to their strong NIR absorption from 700-1300nm. Phase-sensitive detection of the photothermal modulation signal is achieved using a pumped 975 nm laser beam at 80Hz and 160Hz for varying concentrations of PPy nanoparticles dispersed in 2% Intralipid phantom. A phase-sensitive detection system is realised by carrying out the phase calibration using the back reflections obtained from the coverslip used with the sample. This study provides quantitative support for the use of PPy nanoparticles as a potential biocompatible contrast agent in OCT imaging.