Human Serum Albumin Dimerization Enhances the S2 Emission of Bound Cyanine IR806.

Cyanine molecules are important phototheranostic compounds given their high fluorescence yield in the near-infrared region of the spectrum. We report on the frequency and time-resolved spectroscopy of the S2 state of IR806, which demonstrates enhanced emission upon binding to the hydrophobic pocket of human serum albumin (HSA). From excitation-emission matrix spectra and electronic structure calculations, we identify the emission as one associated with a state having the polymethine chain twisted out of plane by 103°. In addition, we find that this configuration is significantly stabilized as the concentration of HSA increases. Spectroscopic changes associated with the S1 and S2 states of IR806 as a function of HSA concentration, as well as anisotropy measurements, confirm the formation of HSA dimers at concentrations greater than 10 µM. These findings imply that the longer-lived S2 state configuration can lead to more efficient phototherapy agents, and cyanine S2 spectroscopy may be a useful tool to determine the oligomerization state of HSA.

Sub-40 fs, 1060-nm Yb-fiber laser enhances penetration depth in nonlinear optical microscopy of human skin.

Advancing the practical utility of nonlinear optical microscopy requires continued improvement in imaging depth and contrast. We evaluated second-harmonic generation (SHG) and third-harmonic generation images from ex vivo human skin and showed that a sub-40 fs, 1060-nm Yb-fiber laser can enhance SHG penetration depth by up to 80% compared to a >100 fs, 800 nm Ti:sapphire source. These results demonstrate the potential of fiber-based laser systems to address a key performance limitation related to nonlinear optical microscopy (NLOM) technology while providing a low-barrier-to-access alternative to Ti:sapphire sources that could help accelerate the movement of NLOM into clinical practice.

Atmospheric pressure femtosecond laser imaging mass spectrometry.

A novel atmospheric pressure imaging mass spectrometry approach that offers improved lateral resolution (10 microm) using near-infrared femtosecond laser pulses for nonresonant desorption and ionization of sample constituents without the need of a laser-absorbing matrix is demonstrated. As a proof of concept the method was used to image a two-chemical pattern in paper. To demonstrate the ability of the approach to analyze biological tissue, a monolayer of onion epidermis was imaged allowing the chemical visualization of individual cells using mass spectrometry at ambient conditions for the first time. As the spatial resolution is currently limited by the limit of detection of the setup (approximately 500 fmol limit of detection for citric acid), improvements in sensitivity will increase the achievable spatial resolution.