Mid-infrared tunable filter based on a femtosecond-written silica volume Bragg grating.

A silica volume Bragg grating (VBG) is used to filter the light of a mid-infrared (mid-IR) supercontinuum laser. The VBG with a 7 µm period was inscribed with 800 nm pulses with a 100 fs duration and the phase-mask technique over a glass thickness of 3 mm. Despite silica's absorption, the VBG allows obtaining a narrowband light source tunable from 2.9 to 4.2 µm with a full width at half maximum (FWHM) of 29 nm. This demonstrates the great potential of using femtosecond-written VBGs as highly tunable, yet selective, spectral filters in the mid-IR.

Duplex Phenotype Detection and Targeting of Breast Cancer Cells Using Nanotube Nanoprobes and Raman Imaging.

We designed, synthesized, and characterized a Raman nanoprobe made of dye-sensitized single-walled carbon nanotubes (SWCNTs) that can selectively target biomarkers of breast cancer cells. The nanoprobe is composed of Raman-active dyes encapsulated inside a SWCNT, whose surface is covalently grafted with poly(ethylene glycol) (PEG) at a density of ∼0.7% per carbon. Using α-sexithiophene- and ß-carotene-derived nanoprobes covalently bound to an antibody, either anti-E-cadherin (E-cad) or anti-keratin-19 (KRT19), we prepared two distinct nanoprobes that specifically recognize biomarkers on breast cancer cells. Immunogold experiments and transmission electron microscopy (TEM) images are first used to guide the synthesis protocol for higher PEG-antibody attachment and biomolecule loading capacity. The duplex of nanoprobes was then applied to target E-cad and KRT19 biomarkers in T47D and MDA-MB-231 breast cancer cell lines. Hyperspectral imaging of specific Raman bands allows for simultaneous detection of this nanoprobe duplex on target cells without the need for additional filters or subsequent incubation steps. Our results confirm the high reproducibility of the nanoprobe design for duplex detection and highlight the potential of Raman imaging for advanced biomedical applications in oncology.

Hyperspectral multiplex single-particle tracking of different receptor subtypes labeled with quantum dots in live neurons.

The efficacy of existing therapies and the discovery of innovative treatments for central nervous system (CNS) diseases have been limited by the lack of appropriate methods to investigate complex molecular processes at the synaptic level. To improve our capability to investigate complex mechanisms of synaptic signaling and remodeling, we designed a fluorescence hyperspectral imaging platform to simultaneously track different subtypes of individual neurotransmitter receptors trafficking in and out of synapses. This imaging platform allows simultaneous image acquisition of at least five fluorescent markers in living neurons with a high-spatial resolution. We used quantum dots emitting at different wavelengths and functionalized to specifically bind to single receptors on the membrane of living neurons. The hyperspectral imaging platform enabled the simultaneous optical tracking of five different synaptic proteins, including subtypes of glutamate receptors (mGluR and AMPAR) and postsynaptic signaling proteins. It also permitted the quantification of their mobility after treatments with various pharmacological agents. This technique provides an efficient method to monitor several synaptic proteins at the same time, which could accelerate the screening of effective compounds for treatment of CNS disorders.

Hyperspectral Microscopy of Near-Infrared Fluorescence Enables 17-Chirality Carbon Nanotube Imaging.

The intrinsic near-infrared photoluminescence (fluorescence) of single-walled carbon nanotubes exhibits unique photostability, narrow bandwidth, penetration through biological media, environmental sensitivity, and both chromatic variety and range. Biomedical applications exploiting this large family of fluorophores will require the spectral and spatial resolution of individual (n,m) nanotube species' fluorescence and its modulation within live cells and tissues, which is not possible with current microscopy methods. We present a wide-field hyperspectral approach to spatially delineate and spectroscopically measure single nanotube fluorescence in living systems. This approach resolved up to 17 distinct (n,m) species (chiralities) with single nanotube spatial resolution in live mammalian cells, murine tissues ex vivo, and zebrafish endothelium in vivo. We anticipate that this approach will facilitate multiplexed nanotube imaging in biomedical applications while enabling deep-tissue optical penetration, and single-molecule resolution in vivo.

High performance resonance Raman spectroscopy using volume Bragg gratings as tunable light filters.

We designed a near infrared tunable resonance Raman spectroscopy system based on a tandem of thick volume Bragg gratings (VBGs). VBGs are here the constituents of two light filtering units: a tunable laser line filter (LLF) and a tunable notch filter (NF). When adapted in a micro-Raman setup with a single stage monochromator (1800 gr/mm grating), the tandem of LLF and NF allowed measurements of Raman signals down to +/-20 cm(-1). The good performance and fast tunability of the VBG Raman system was demonstrated on a sulfur powder and on a bulk single-walled carbon nanotube sample through a series of 22 Stokes and anti-Stokes spectra recorded at excitation wavelengths between 800 and 990 nm. The main drawbacks of the setup are the limited spectral range to the near infrared and the small angular acceptance of the filters (approximately 1 mrad), which causes mainly attenuation problems with the NF. The impact of the main limitations is discussed and solutions are provided.