Depth profiling of gold nanoparticles and characterization of point spread functions in reconstructed and human skin using multiphoton microscopy

Abstract

Multiphoton microscopy has become popular in studying dermal nanoparticle penetration. This necessitates studying the imaging parameters of multiphoton microscopy in skin as an imaging medium, in terms of achievable detection depths and the resolution limit. This would simulate real-case scenarios rather than depending on theoretical values determined under ideal conditions. This study has focused on depth profiling of sub-resolution gold nanoparticles (AuNP) in reconstructed (fixed and unfixed) and human skin using multiphoton microscopy. Point spread functions (PSF) were determined for the used water-immersion objective of 63×/NA = 1.2. Factors such as skin-tissue compactness and the presence of wrinkles were found to deteriorate the accuracy of depth profiling. A broad range of AuNP detectable depths (20-100 μm) in reconstructed skin was observed. AuNP could only be detected up to ∼14 μm depth in human skin. Lateral (0.5 ± 0.1 μm) and axial (1.0 ± 0.3 μm) PSF in reconstructed and human specimens were determined. Skin cells and intercellular components didn't degrade the PSF with depth. In summary, the imaging parameters of multiphoton microscopy in skin and practical limitations encountered in tracking nanoparticle penetration using this approach were investigated.

Setup for investigating gold nanoparticle penetration through reconstructed skin and comparison to published human skin data

“…This technique is referred to as multiphoton-absorption-induced luminescence (MAIL), where the absorption of multiple photons from a near-infrared pulsed femtosecond laser can lead to robust luminescence of metal nanoparticles. 8,[23][24][25][26] Multiphoton microscopy was therefore employed as a useful optical technique to track particle penetration in skin 8,22,[26][27][28] and was the imaging tool in our study to track model AuNP.…”

“…This data would then allow comparison of results obtained using SE with previous experiments on full-thickness HS we conducted with the same particles in our laboratory, 7,8 thus eliminating inter-laboratory variations. AuNP were chosen as a good model for studying skin penetration of nanoparticles due to their unique optical properties 23,26,29,30 in addition to their potential as drug carriers.…”

Lipid-coated gold nanocomposites for enhanced cancer therapy

“…29,30 Colloidal nanoparticle-based drug delivery has been considered as a potential tool with remarkable abilities in cancer imaging and therapeutics. [31][32][33][34][35][36] Encapsulating nanoparticles in lipid vehicles is an alternative approach that has been used in recent years to achieve controlled drug delivery and implement combined therapy. Therefore, the co-delivery of drug and nanoparticle is becoming a standard strategy in cancer therapy, since it substantially reduces the necessary DTX dose and improves …”

Accumulating advantages, reducing limitations: Multimodal nonlinear imaging in biomedical sciences – The synergy of multiple contrast mechanisms

“…While multiphoton fluorescence is fully compatible with labels used for single photon fluorescence, novel nanoparticles provide extremely bright luminescence signals and low photobleaching. Gold nanoparticles are bright luminescent structures but of low toxicity [68,69] suited for depth profiling of human skin [70]. Quantum dots made of CdTe are also bright, have broad excitation and narrow emission spectral widths and high photostability.…”

“…A combination of drug delivery and tissue engineering, i.e., the dermal penetration of gold nanoparticles, has been studied in human and reconstructed skin [70]. Also in other investigations multimodal nonlinear microscopy has been used as a versatile tool to investigate artificial tissues, i.e., tissue engineered materials [109][110][111][112][113].…”