Phase-sensitive OCT imaging of multiple nanoparticle species using spectrally multiplexed single pulse photothermal excitation

Abstract

We apply phase-sensitive optical coherence tomography to image multiple nanoparticle species with two excitation wavelengths matched to their distinct absorption peaks. Using different modulation frequencies, multiple species collocated within the sample can be distinguished. In addition, we characterize single-pulse excitation schemes as a method to minimize bulk heating of the sample. We demonstrate this new scheme with B-mode photothermal measurements of tissue phantoms.

Keywords: (110.3000) Image quality assessment; (160.4236) Nanomaterials; (170.4500) Optical coherence tomography.

Fig. 1

(a) Schematic of the phase-sensitive photothermal SDOCT system (b) Typical OCT B-mode image of human epithelium (c) Measured absorption spectra of gold (60 nm diameter) and silver (40 nm diameter) nanospheres (d) Sample preparation

Fig. 2

(a) Measured phase from the agar sample without photothermal modulation. (b) Measured phase (inset) and Fourier transforms of the measured phase from the agar sample with simulations amplitude modulation of excitation for gold and silver nanoparticles. (c) Measured phase with amplitude modulation of gold nanoparticles and the measured phase (inset) at equilibrium, showing sample heating. (d) Measured phase with a 400 μs width single-pulse excitation and measured phase with a 400 μs width pulse excitation with repetition period of 1 second. Note the phase rapidly returns to baseline after excitation.

Fig. 3

(a) Amplitude in Fourier domain for different concentrations of gold and silver nanoparticles (N = 5 measurements for each point) (b) Measured SNR for different pulse duration (gold nanoparticles, N = 5)

Fig. 4

(a) Tissue phantom scheme showing a region containing nanoparticles and a region without nanoparticles (b) A typical OCT B-mode image of the tissue phantom (c) Measured phase response to the single-pulse excitation in the ROI containing gold nanoparticles and measured phase response to the single-pulse excitation in the ROI without gold nanoparticles (d) A typical OCT b- mode image of the tissue phantom false colored (e) B-mode time scan of the tissue phantom