We report the in situ detection of amorphous hydrated silica in the Bills Bay abrasion patch, located in the eastern portion of the Margin Unit between the rim of Jezero crater and the western delta. Here, hydrated silica co-occurs with olivine, Fe-Mg carbonates, secondary Fe-Mg silicates, and hydrated Mg-sulfate as determined by UV Raman (SHERLOC) and X-ray fluorescence (PIXL) spectrometers onboard the Perseverance rover. Almost pure hydrated silica fills the intergranular space between olivine and carbonate-bearing domains. We performed Raman analysis of terrestrial opals with various crystallinities including opal-AN, AG, CT, and C. We found that the Si-O symmetric stretching Raman band at similar to 800 cm-1 is sensitive to opal crystallinity, yet insensitive to ambient temperature (at similar to 77-293 K) and silica hydration. We identified the crystal structure of the Bills Bay Hydrated Silica (BBHS) as opal-A. Furthermore, we developed a Raman methodology to quantify opal-A hydration. We found that the total amount of hydration in the BBHS phases was 1.7 +/- 0.2 wt. %. Most of this hydration, 1.5 +/- 0.2 wt. %, reflects the presence of silanol groups. Our analysis revealed that the Raman spectrum of BBHS closely resembles that of opal-A that has lost most of its molecular water. The composition and textures of the Bills Bay abrasion indicate that BBHS is derived from olivine carbonation. Opal-A is the only silica polymorph identified in the SHERLOC data. We hypothesized that silica precipitation occurred, either during the late stages of a major carbonation event or during a brief, subsequent aqueous alteration event unrelated to carbonation.

A combination of a highly efficient 213 nm Rayleigh rejection filter (RRF) and a miniaturized 213 nm neodymium-doped vanadate laser enables portable deep ultraviolet (UV) Raman spectrometers. We demonstrate the high efficiency of 213 nm RRF manufactured by Green Optics Co., Ltd. by utilizing our compact 213 nm vanadate laser to measure high signal-to-noise ratio UV Raman spectra of Teflon and UV resonance Raman (UVRR) spectra of solid ammonium nitrate. We also demonstrate UVRR detection of trace amounts of ammonia formed during ammonium nitrate UV photolysis. We roughly estimate the ammonia UVRR detection limit of ∼10 ng under our experimental conditions.

We utilize a novel, high-power, tunable, continuous wave (CW) deep UV laser to measure resonance Raman spectra of phenolate solutions with high signal-to-noise ratios (SNR). In UV resonance Raman (UVRR), increased coupling of the excitation light with a chromophore can transfer molecules into excited states that cause increased heating and photochemistry. Deep UV lasers have traditionally utilized high peak powers to enable efficient single-pass nonlinear conversion from visible into near infrared light. Nonlinear phenomena such as the formation of transient radical species, Raman saturation, thermal heating, and dielectric breakdown can introduce extraneous light sources that can complicate the interpretation of the Raman spectrum. Dielectric breakdown can increase the baseline, increase noise, and sometimes saturate the detector, preventing Raman detection. Spontaneous Raman scattering intensities should scale linearly with the excitation light intensity. However, this linear behavior does not always occur with pulsed laser excitation. This occurs because stimulated Raman scattering can cause a superlinear intensity response, or transient absorption can cause sublinear intensity responses. CW laser excitation excites samples with electric fields that are much lower than typical pulsed laser excitation. This eliminates the nonlinear responses. The geometry of our new CW laser enables high gain in the harmonic generation cavities that achieve high harmonic generation efficiencies. Average power in the deep UV is >30 mW for wavelengths as short as 206 nm. In the work here, we demonstrate that CW excitation is ideal for resonance Raman measurements in general to reduce spectral complexity.

We developed a state-of-the-art, high-sensitivity, low-stray-light standoff deep-ultraviolet (DUV) Raman spectrometer for the trace detection of resonance Raman-enhanced chemical species. As an excitation source for Raman measurements, we utilized our recently developed, second-generation, miniaturized, diode-pumped, solid-state neodymium-doped gadolinium orthovanadate (Nd:GdVO 4 ) laser that generates quasi-continuous wave 228 nm light. This 228 nm excitation enhances the Raman intensities of vibrations of NO x groups in explosive molecules, aromatic groups in biological molecules, and various aromatic hydrocarbons. Our DUV Raman spectrograph utilizes a custom DUV f/8 Cassegrain telescope with an ∼200 mm diameter primary mirror, high-efficiency DUV transmission gratings, custom DUV mirrors, and a custom 228 nm Rayleigh rejection filter. We utilized our new standoff DUV Raman spectrometer to measure high signal-to-noise ratio spectra of ∼50 μg/cm 2 drop-cast explosives: ammonium nitrate (AN), trinitrotoluene, pentaerythritol tetranitrate as well as aromatic biological molecules: lysozyme, tryptophan, tyrosine, deoxycytidine monophosphate, deoxyadenosine monophosphate at an ∼3 m distance within 10–30 s accumulation times. We roughly estimate the average ultraviolet resonance Raman (UVRR) detection limits for the relatively homogeneous drop-cast films of explosives and biological molecules to be ∼1 μg/cm 2 when utilizing a continuous raster scanning that averages Raman signal over ∼1 cm 2 sample area to avoid quick analyte depletion due to ultraviolet (UV) photolysis. We determined 3 m standoff UVRR detection limits for drop-cast AN films and identified factors impacting UVRR detection limits such as analyte photochemistry and analyte morphology. We found a detection limit of ∼0.5 μg/cm 2 for drop-cast AN films on glass substrates when the Raman signal is averaged over ∼0.5 cm 2 of sample surface using a continuous raster scan. For a step raster scan, when the probed sample area is limited to the laser spot size, the detection limit is approximately tenfold higher (∼5 μg/cm 2 ) due to the impact of UV photochemistry.

The presence and distribution of preserved organic matter on the surface of Mars can provide key information about the Martian carbon cycle and the potential of the planet to host life throughout its history. Several types of organic molecules have been previously detected in Martian meteorites 1 and at Gale crater, Mars 2 – 4 . Evaluating the diversity and detectability of organic matter elsewhere on Mars is important for understanding the extent and diversity of Martian surface processes and the potential availability of carbon sources 1 , 5 , 6 . Here we report the detection of Raman and fluorescence spectra consistent with several species of aromatic organic molecules in the Máaz and Séítah formations within the Crater Floor sequences of Jezero crater, Mars. We report specific fluorescence-mineral associations consistent with many classes of organic molecules occurring in different spatial patterns within these compositionally distinct formations, potentially indicating different fates of carbon across environments. Our findings suggest there may be a diversity of aromatic molecules prevalent on the Martian surface, and these materials persist despite exposure to surface conditions. These potential organic molecules are largely found within minerals linked to aqueous processes, indicating that these processes may have had a key role in organic synthesis, transport or preservation.

Aptamer-functionalized two-dimensional photonic crystal (2DPC) hydrogels are reported for the detection of adenosine (AD). As a molecular recognition group, an AD-binding aptamer was covalently attached to 2DPC hydrogels. This aptamer selectively and sensitively binds AD, changing the conformation of the aptamer from a long single-stranded structure (AD-free conformation) to a short hairpin loop structure (AD-bound conformation). The AD-binding-induced changes of aptamer conformation reduced the volume of the 2DPC hydrogels and decreased the interparticle spacing of the 2DPC embedded in the hydrogel network. The particle spacing changes being dependent on AD concentration were determined by measuring 2DPC light diffraction using a simple laser pointer. The 2DPC hydrogel sensor showed a large particle spacing decrease of 110 nm in response to 1 mM AD in phosphate-buffered saline (PBS). The linear range of determination of AD was 0.1 nM to 1 mM and the limit of detection was 0.09 nM. The hydrogel sensor response for real samples was then validated in diluted fetal bovine serum (FBS) and human urine. The average

There is a need to develop versatile sensing motifs that can be used to detect a variety of chemical targets in resource-limited settings, for example, at the point of care. While numerous sensing technologies have been developed toward this effort, these technologies can be overly complex and require a skilled technician, extensive sample preparation, or sophisticated instrumentation to use, limiting their generalizability and application in resource-limited settings. Here, we report a novel sensing motif that utilizes DNA-crosslinked two-dimensional photonic crystal (2DPC) hydrogels. These hydrogel sensors contain a DNA aptamer recognition group that binds a target analyte. As proof of concept, we fabricated 2DPC hydrogels using a well-studied adenosine-binding aptamer. This adenosine aptamer is duplexed with a partially complementary strand and forms responsive crosslinks in the hydrogel polymer network. When adenosine is introduced, aptamer-adenosine binding occurs, breaking the DNA crosslinks and causing the hydrogel to swell. This in turn increases the particle spacing of an embedded 2DPC array, shifting the 2DPC Bragg diffraction. Thus, adenosine concentration can be monitored through 2DPC Bragg diffraction measurements. A linear range of 20 μM to 2 mM was observed. The detection limits were calculated to be 13.9 μM in adenosine-binding buffer and 26.7 μM in fetal bovine serum. This reported sensing motif has a readout that is simple and rapid and requires minimal equipment. We hypothesize that this sensing motif is generalizable and that other sensors can be easily fabricated by simply exchanging the aptamer that serves as a molecular recognition group.

UV resonance Raman spectroscopy is uniquely suitable for standoff measurements due to its high sensitivity and selectivity. When excitation wavelength falls within an electronic transition of a molecule, Raman band intensities associated with the chromophore vibrations are significantly enhanced. This resonance Raman Effect, as well as negligible fluorescence interference in the deep UV, enable the detection and investigation of enhanced species at trace concentrations at a distance. We developed a state-of-the-art, high-efficiency standoff deep UV Raman spectrometer. This spectrometer is based on a custom deep UV F/8 Cassegrain telescope with a 200 mm primary mirror. This telescope is equipped with an electric secondary focus operating from infinity to 3 m distance. The UV Raman spectrograph utilizes high-efficiency deep UV transmission grating and custom Rayleigh rejection filter. As an excitation source for Raman measurements, we utilized a recently developed 228 nm compact solid state deep UV laser. The 228 nm resonance excitation enhances the Raman intensities of vibrations of NOx groups, peptide bonds, aromatic amino acid side chains, and DNA/RNA nucleotides. We used this novel spectrometer for detection of NOx-based explosive materials at trace concentrations at a stand-off distance.

We describe the wavelength calibration of the spectrometer for the scanning of habitable environments with Raman and luminescence for organics and chemicals (SHERLOC) instrument onboard NASA’s Perseverance Rover. SHERLOC utilizes deep ultraviolet Raman and fluorescence (DUV R/F) spectroscopy to enable analysis of samples from the Martian surface. SHERLOC employs a 248.6 nm deep ultraviolet laser to generate Raman-scattered photons and native fluorescence emission photons from near-surface material to detect and classify chemical and mineralogical compositions. The collected photons are focused on a charge-coupled device and the data are returned to Earth for analysis. The compact DUV R/F spectrometer has a spectral range from 249.9 nm to 353.6 nm (∼200 cm −1 to 12, 000 cm −1 ) (with a spectral resolution of 0.296 nm (∼40 cm −1 )). The compact spectrometer uses a custom design to project a high-resolution Raman spectrum and a low-resolution fluorescence spectrum on a single charge-coupled device. The natural spectral separation enabled by deep ultraviolet excitation enables wavelength separation of the Raman/fluorescence spectra. The SHERLOC spectrometer was designed to optimize the resolution of the Raman spectral region and the wavelength range of the fluorescence region. The resulting illumination on the charge-coupled device is curved, requiring a segmented, nonlinear wavelength calibration in order to understand the mineralogy and chemistry of Martian materials.

There is a need to develop at-home phenylalanine (Phe) test kits, analogous to home glucose meters, for phenylketonuria patients who must measure their blood Phe levels frequently to adjust their diet. Unfortunately, such test kits are not available yet because of the lack of simple and inexpensive Phe-sensing elements. With the goal of developing a Phe-sensing element, we fabricated two-dimensional photonic crystal (2DPC) hydrogels that quantify human serum phenylpyruvate (PhPY), which is the product of the reaction between Phe and the enzyme phenylalanine dehydrogenase. The PhPY-sensing hydrogels have oxyamine recognition groups that link PhPY to the hydrogel polymer network via chemoselective oxime ligation. This structural modification induces the hydrogel to swell, which then increases interparticle spacings within the embedded 2DPC. The PhPY-induced particle spacing changes are measured from light diffraction and used to quantify the PhPY concentrations. The estimated limit of detection of PhPY in human serum for a detection time of 30 min is 19 μM, which is comparable to the minimum blood Phe concentrations of healthy people. Besides the potential application for developing Phe-sensing elements, this new hydrogel sensing approach via chemoselective oxime ligation is generalizable to the development of other chemical sensors working in complex biological environments.

The fabrication of highly ordered similar to 2 mu m thick silica inverse opal (IO) photonic crystal (PhC) films is reported. These IO films diffract deep ultraviolet light (UV, <250 nm) and are prepared using the inward-growing self-assembly of similar to 143 nm diameter monodisperse polystyrene nanoparticles (PSNPs) suspended within a hydrolyzed silicate sol-gel precursor solution. Removal of the PSNPs results in solid, robust IOs that attenuate >70% of light meeting the Bragg condition at normal incidence. Structural and optical characterization of these silica IO films indicate that noncoherent scattering losses are low at deep UV wavelengths, even though substantial crack-type defects occur. The IO films exhibit a diffraction fwhm of similar to 12 nm with diffraction efficiencies of >30% for 213 nm laser light and possess nanoscale porosities of similar to 20 nm. Relative to reported silica IOs that diffract deep UV light, these new PhC materials show at least 28% narrower spectral bandwidths and 5-fold increased diffraction efficiencies. We postulate that increased ordering of the silica network is the principal factor that improves the optical performance. Furthermore, the relatively flat, homogeneous IO film surfaces produce narrow, symmetric diffraction beams suitable for optical imaging applications. Strategies to further improve the diffraction efficiencies of these silica IO materials and the implications for novel technological applications are discussed.

We describe a new compact diode-pumped solid-state frequency quadrupled quasi-three-level neodymium-doped gadolinium vanadate (Nd:GdVO4) laser that generates similar to 50 mW of 228-nm quasi-continuous wave light as ns pulses at a tunable kilohertz repetition rate. We developed two generations of this laser. The first generation has a high duty cycle and a tunable repetition rate. The second generation is optimized for maximum output power. We utilize these new lasers to measure ultraviolet resonance Raman (UVRR) spectra of many important chromophores that absorb in deep ultraviolet (UV). We demonstrate the utility of this excitation by measuring the 228-nm absolute differential Raman cross sections of explosives, peptides, aromatic amino acids, and DNA/RNA nucleotides. Deep UV excitation at 228 nm occurs within the pi -> pi* electronic transitions of these molecules. The 228-nm resonance excitation enhances the Raman intensities of vibrations of NO(x)groups, peptide bonds, aromatic amino acid side chains, and DNA/RNA nucleotides. The measured 228-nm UVRR cross sections of these molecules are 10(3)-10(4)fold greater than those excited in the visible spectral region. These new lasers should be of great interest for UVRR spectroscopy and for other applications that benefit from compact, high average power deep UV laser light sources with low peak powers.

Responsive pure protein organogel sensors and catalysts are fabricated by replacing the aqueous mobile phase of protein hydrogels with pure ethylene glycol (EG). Exchanging water for EG causes irreversible volume phase transitions (VPT) in bovine serum albumin (BSA) polymers; however, BSA hydrogel and organogel sensors show similar volume responses to protein-ligand binding. This work elucidates the mechanisms involved in this enabling irreversible VPT by examining the protein secondary structure, hydration, and protein polymer morphology. Organogel proteins retain their native activity because their secondary structure and hydration shell are relatively unperturbed by the EG exchange. Conversely, the decreasing solvent quality initiates polymer phase separation to minimize the BSA polymer surface area exposed to EG, thus decreasing distances between BSA polymer strands. These protein polymer morphology changes promote interprotein interactions between BSA polymer strands, which increase the effective polymer cross-link density and prevent organogel swelling as the mobile phase is exchanged back to water.

Due to its high sensitivity and selectivity, UV resonance Raman (UVRR) spectroscopy has a number of scientific and industrial applications. Deep UVRR excited within explosive absorption bands (200 – 230 nm) enables trace explosive detection at a distance due to the resonance enhancement of Raman band intensities, stronger light scattering at short wavelengths, as well as negligible florescence interference. We are developing deep UVRR detection methodologies by investigating resonance enhancement of explosives excited in the deep UV, determining the optimal excitation wavelengths, investigating explosive UV-photochemistry, characterizing explosive UV photoproducts, and measuring UVRR spectral evolution during explosive photolysis. We are also developing state-of-the-art UVRR instrumentation by designing and manufacturing high efficiency, high throughput standoff UVRR spectrometers, co-developing new compact solid state deep UV lasers, and designing novel deep UV optical diffracting devices.

Expanded polyglutamine (polyQ) tracts in proteins, which are known to induce their aggregation, are associated with numerous neurodegenerative diseases. Longer polyQ tracts correlate with faster protein aggregation kinetics and a decreased age of onset for polyQ disease symptoms. Here, we use UV resonance Raman spectroscopy, circular dichroism spectroscopy, and metadynamics simulations to investigate the solution-state structures of the D2Q15K2 (Q15) and D2Q20K2 (Q20) peptides. Using metadynamics, we explore the conformational energy landscapes of Q15 and Q20 and investigate the relative energies and activation barriers between these low-energy structures. We compare the solution-state structures of D2Q10K2 (Q10), Q15, and Q20 to determine the dependence of polyQ structure on the Q tract length. We show that these peptides can adopt two distinct monomeric conformations: an aggregation-resistant PPII-like conformation and an aggregation-prone β-strand-like conformation. We find that longer polyQ peptides have an increased preference for the aggregation-prone β-strand-like conformation. This preference may play an important role in the increased aggregation rate of longer polyQ peptides that is thought to lead to decreased neurodegenerative disease age of onset for polyQ disease patients.

Utilizing protein chemistry in organic solvents has important biotechnology applications. Typically, organic solvents negatively impact protein structure and function. Immobilizing proteins via cross-links to a support matrix or to other proteins is a common strategy to preserve the native protein function. Recently, we developed methods to fabricate macroscopic responsive pure protein hydrogels by lightly cross-linking the proteins with glutaraldehyde for chemical sensing and enzymatic catalysis applications. The water in the resulting protein hydrogel can be exchanged for organic solvents. The resulting organogel contains pure organic solvents as their mobile phases. The organogel proteins retain much of their native protein function, i.e., protein-ligand binding and enzymatic activity. A stepwise ethylene glycol (EG) solvent exchange was performed to transform these hydrogels into organogels with a very low vapor pressure mobile phase. These responsive organogels are not limited by solvent/mobile phase evaporation. The solvent exchange to pure EG is accompanied by a volume phase transition (VPT) that decreases the organogel volume compared to that of the hydrogel. Our organogel sensor systems utilize shifts in the particle spacing of an attached two-dimensional photonic crystal (2DPC) to report on the volume changes induced by protein-ligand binding. Our 2DPC bovine serum albumin (BSA) organogels exhibit VPT that swell the organogels in response to the BSA binding of charged ligands like ibuprofen and fatty acids. To our knowledge, this is the first report of a pure protein organogel VPT induced by protein-ligand binding. Catalytic protein organogels were also fabricated that utilize the enzyme organophosphorus hydrolase (OPH) to hydrolyze toxic organophosphate (OP) nerve agents. Our OPH organogels retain significant enzymatic activity. The OPH organogel rate of OP hydrolysis is ∼160 times higher than that of un-cross-linked OPH monomers in a 1:1 ethylene glycol/water mixture.

Fibrillization of polyglutamine (polyQ) tracts in proteins is implicated in at least 10 neurodegenerative diseases. This generates great interest in the structure and the aggregation mechanism(s) of polyQ peptides. The fibrillization of polyQ is thought to result from the peptide's insolubility in aqueous solutions; longer polyQ tracts show decreased aqueous solution solubility, which is thought to lead to faster fibrillization kinetics. However, few studies have characterized the structure(s) of polyQ peptides with low solubility. In the work here, we use UV resonance Raman spectroscopy to examine the secondary structures, backbone hydrogen bonding, and side chain hydrogen bonding for a variety of solution-state, solid, and fibril forms of D2Q20K2 (Q20). Q20 is insoluble in water and has a β-strand-like conformation with extensive inter- and intrapeptide hydrogen bonding in both dry and aqueous environments. We find that Q20 has weaker backbone-backbone and backbone-side chain hydrogen bonding and is less ordered compared to that of polyQ fibrils. Interestingly, we find that the insoluble Q20 will form fibrils when incubated in water at room temperature for ∼5 h. Also, Q20 can be prepared using a well-known disaggregation procedure to produce a water-soluble PPII-like conformation with negligible inter- and intrapeptide hydrogen bonding and a resistance to aggregation.

We demonstrate deep ultraviolet (UV) photoacoustic spectroscopy (PAS) of trace explosives using a sensitive microphone at meter standoff distances. We directly detect 10 µg/cm2 of pentaerythritol tetranitrate (PETN), 2,4,6-trinitrotoluene (TNT), and ammonium nitrate (AN) with 1 s accumulations from a 3 m standoff distance. Large PAS signals for standoff detection are achieved by exciting into the absorption bands of the explosives with a 213 nm laser. We also investigate the impact of the deep UV photochemistry of AN on the PAS signal strength and stability. We find that production of gaseous species during photolysis of AN enhances the PAS signal strength. This deep UV photochemistry can, however, limit the PAS signal lifetimes when detecting trace quantities.

We fabricated the first solid, mechanically robust inverse opal photonic crystals that diffract in the deep ultraviolet (UV) spectral region. These photonic crystals are fabricated by self-assembling <140 nm diameter monodisperse polystyrene nanoparticles into face centered cubic 3D close packed structures on fused silica microscope slides in the presence of tetraethyl orthosilicate via a vertical deposition method. Tetraethyl orthosilicate condenses in the nanoparticle interstices during self-assembly, immobilizing the polystyrene nanoparticles in an SiO2 matrix. Removal of the polystyrene nanoparticles using piranha solution yields a stable SiO2 inverse opal structure that Bragg diffracts in the deep UV at <245 nm. We measured the UV-vis transmission, diffraction of a collimated deep UV white light source, and diffraction of 229 nm laser light in order to characterize the deep UV optical performance of these photonic crystals. We measured a maximum light attenuation of similar to 98% at the Bragg condition, calculated a photonic crystal thickness of similar to 33 layers, and calculated a diffraction spectral bandwidth of 16.8 nm full-width at half-maximum. The mechanical robustness, photochemical durability, and shelf life of the deep UV diffracting photonic crystals demonstrated in this work enable their development for use as deep UV optical devices. We conclude that additional optimization of the self-assembly and vertical deposition conditions is required to improve the thickness uniformity and ordering of these photonic crystals to increase their diffraction efficiency and to decrease their diffraction bandwidth.

The best-known examples of smart, responsive hydrogels derive from poly( N-isopropylacrylamide) (PNIPAM) cross-linked polymer networks. These hydrogels undergo volume phase transitions (VPTs) triggered by temperature, chemical, and/or environmental changes. PNIPAM hydrogels can undergo more than 50-fold volume changes within ∼1 μs intervals. Studies have tried to elucidate the molecular mechanism of these extraordinarily large responses. Nevertheless, the molecular reaction coordinates that drive the VPT remain unclear. Using visible nonresonance Raman temperature-jump spectroscopy, we determined the molecular ordering of this VPT. The PNIPAM hydrophobic isopropyl and methylene groups dehydrate with time constants of 109 ± 64 and 104 ± 44 ns, initiating the volume collapse of PNIPAM. The subsequent dehydration of the PNIPAM amide groups is significantly slower, as our group previously discovered (360 ± 85 ns). This determination of the ordering of the molecular reaction coordinate of the PNIPAM VPT enables the development of the next generation of super-responsive materials.