Near-infrared absorbing polymer nano-particle as a sensitive contrast agent for photo-acoustic imaging

Abstract

Polymer nano-particles (PNPs) with a near-infrared (NIR) light absorption were prepared by the nano-emulsion method to develop contrast agents for photo-acoustic (PA) imaging. The PNP containing silicon naphthalocyanine showed a high absorption coefficient up to 10(10) M(-1) cm(-1). This is comparable to plasmonic gold nano-particles, which have been studied as PA contrast agents. For the PNP larger than 100 nm, the enhancement of the PA signal was observed compared to the gold nano-particle with a similar absorption coefficient and size. In the case of the PNP, the heat by the light absorption is confined in the particle due to the low thermal diffusivity of polymer materials. We showed that the strong thermal confinement effect of PNP results in the enhancement of the efficiency of the PA signal generation and that the PA intensity can be enhanced by the increase of the Grüneisen parameter of the matrix polymer of PNP. The PA signal from the PNP of poly(methyl methacrylate) was 9-fold larger than that of gold nano-particles with the same absorption coefficient. We demonstrated that in the in vivo PA imaging the detection limit of PNP was of the order of 10(-13) M. The NIR absorbing PNP will be a promising candidate of a sensitive contrast agent for PA imaging.

Contrast agents for molecular photoacoustic imaging

“…Despite their early stage of development, polymers and encapsulations have been demonstrated in numerous passive targeting applications: imaging mouse brain vasculature 102,111 and tumor sentinel lymph node identification 104,112,105 as well as primary tumor characterization [113][114][115] . Wang et al actively targeted folate receptor positive MCF-7 breast cancer xenografts with poly(D,L-lactide-co-glycolide) (PLGA) lipid NP containing ICG for PA signal and folic acid for targeting (Fig.…”

Laser generated gold nanocorals with broadband plasmon absorption for photothermal applications

“…[11][12][13] For instance, networks of partially fused gold nanoparticles showed very low-energy surface plasmon modes capable of supporting long-range and spectrally tunable propagation in nanoscale waveguides. 6,9,16 There is a long list of applications possible for Au nanostructures with efficient absorption in the visible and NIR, such as in light induced vapour generation, 17 plasmon enhanced catalysis, 18 photothermal polymerization, 19 antimicrobial systems, 20, 21 photoacoustic imaging, 22,23 light triggered drug release 24,25 and photothermal therapy. The interest in 1D Au nanoassemblies is due also to the their potential exploitability as intermediate steps for the fabrication of nanowires.…”

“…10,26,27 For instance, the recent theoretical prediction of efficiencies up to 85% is fostering the development of plasmon thermophotovoltaic systems based on materials which are chemically stable at high temperatures and have broadband optical absorption. 22,23 A key empowering feature in this field is the development of broadband red-NIR contrast agents for multispectral photoacoustic imaging. 26 For instance, NIR absorbing nanoparticles are exploitable as sensitizers for photothermal therapy, which is based on the occurrence of protein denaturation and cellular membrane disruption, with initiation of apoptotic mechanisms, when tissues temperature exceeds 42 -44 °C.…”

Organic/polymer photothermal nanoagents for photoacoustic imaging and photothermal therapy in vivo

“…Nanomaterials, in particular the nanoparticles (NPs) have shown unique merits such as improved water-solubility of payload, prolonged blood circulation time and enhanced permeability and retention (EPR) effect [3,[25][26][27]. To date, a variety of photothermal nanoagents for PA imaging and PTT have been reported, including NPs based on noble metal materials and transition metal dichalcogenides, carbon nanomaterials and organic/polymer-based NPs [28][29][30][31][32][33][34][35][36][37][38][39][40][41]. While these photothermal nanoagents have their own merits, each has a drawback.…”

“…The PA and PTT efficiencies of the organic/polymer photothermal nanoagents are significantly affected by their extinction coefficients, non-radiative decay efficiencies and Grüneisen coefficients [33]. By improving any of these above parameters, massive researches have been proven to improve the PA imaging and PTT effect [34][35][36][37][38][39]. Organic/polymer photothermal nanoagents utilized in PA imaging and PTT could be roughly divided into two main groups: semiconducting polymer NPs (SPNs) and small-molecule organic photothermal agents-encapsulated NPs [46,47].…”