SU-8 photoresist has been applied to three-dimensional (3D) patterning of photonics, micro/nanoelectromechanical systems and microfluidics. SU-8 photoresist can be patterned by absorption of ultraviolet radiation using a photomask; however, diffraction effects in the bulk resist and the use of a 2D mask limits complex 3D structure design. Direct laser writing (DLW) using multiphoton absorption can produce complex, sub-diffraction limited structures in the resist, but controlling DLW in SU-8 is complicated by many competing processes. Using 100 fs pulses at 1.7 μm, we reliably develop SU-8 photoresist via femtosecond optical curing on glass substrate and avoid competition from two, three, and four photon absorption processes. We verify optical curing of the resist by developing the resist without a post-bake.
Raman spectroscopy is an essential optical tool for molecular fingerprints. The vibrational modes of biologically important molecules including proteins, nucleic acids and lipids have been studied to provide insight into their structure as well as insight into the metabolic processes and biomarker expression of cells. To explore hyper-Raman scattering as a complementary technique to Raman scattering, we build a laser system that can perform Raman and hyper-Raman scattering studies using a single setup. Using three amplification stages we are able to generate 8 ps, 1064 nm pulses at repetition rates up to 30 MHz. Converting the 1064 nm source laser to 532 nm, we achieve fast hyper-Raman detection and collect our spectrum with a commercial spectrometer and CCD. Using a single optical setup, we collect and compare Raman spectra at 532 nm to hyper-Raman spectra at 266 nm for water, ethanol and L-tartaric acid. Furthermore, we observe changes in the hyper-Raman peak intensities of an aqueous L-tartaric acid solution when selecting different laser repetition rates highlighting the need to control laser power and repetition rate to identify and mitigate thermal effects in biomolecules.
Low frequency Raman spectroscopy is a highly sensitive and non-destructive technique used to investigate the vibrational and rotational modes of biological and non-biological materials. The Raman spectra measured provide information about the chemical structure and nature of these materials. In this study, we present the design and construction of a low frequency Raman spectroscopy system that is able to measure signals <10 cm-1 to <400 cm-1. The system consisted of a 514.5nm monochromatic laser directed through a polarizing beam cube and half waveplate to adjust the intensity of the beam. The beam was expanded and reflected off a 514.5 nm high pass filter before passing through a 50x Mitutoyo objective, which focuses it onto the sample. The back scattered light was recollimated through the objective. The high pass filter and three 514.5 nm Bragg filters were used to reduce the Rayleigh signal. The remaining Raman signal was focused into a Shamrock 303i spectrometer with a cooled ANDOR CCD camera. Using high dynamic range data acquisition with background subtraction, this system allowed low frequency Raman spectroscopy of reduced cytochrome C, bovine serum albumin, microtubules and collagen in solution. The system has the advantage of enabling the measurement of the low frequency Raman signal without sacrificing the ability to perform traditional Raman spectroscopy.
Raman and Brillouin spectroscopy are powerful tools for non-invasive and non-destructive investigations of material chemical and mechanical properties. In this study, we use a newly developed custom-built dual Raman-Brillouin microspectroscopy instrument to build on previous works studying in-vivo stress response of live plants using only a Raman spectroscopy system. This dual Raman-Brillouin spectroscopy system is capable of fast simultaneous spectra acquisition from single-point locations. Shifts and changes in a samples Brillouin spectrum indicate a change in the physical characteristics of the sample, namely mechano-elasticity; in measuring this change, we can establish a relationship between the mechanical properties of a sample and known stress response agents, such as reactive oxygen species and other chemical constituents as indicated by peaks in the Raman spectra of the same acquisition point. Simultaneous application of these spectroscopic techniques offers great promise for future development and applications in agricultural and biological studies and can help to improve our understanding of mechanochemical changes of plants and other biological samples in response to environmental and chemically induced stresses at microscopic or cellular level.
Recent developments in understanding of nanomaterial behaviors and synthesis have led to their application across a wide range of commercial and scientific applications. Recent investigations span from applications in nanomedicine and the development of novel drug delivery systems to nanoelectronics and biosensors. In this study, we propose the application of a newly engineered temperature sensitive water-based bio-compatible core/shell up-conversion nanoparticle (UCNP) in the development of a smart substrate for remote temperature sensing. We developed this smart substrate by dispersing functionalized nanoparticles into a polymer solution and then spin-coating the solution onto one side of a microscope slide to form a thin film substrate layer of evenly dispersed nanoparticles. By using spin-coating to deposit the particle solution we both create a uniform surface for the substrate while simultaneously avoid undesired particle agglomeration. Through this investigation, we have determined the sensitivity and capabilities of this smart substrate and conclude that further development can lead to a greater range of applications for this type smart substrate and use in remote temperature sensing in conjunction with other microscopy and spectroscopy investigations.