Probe Volume Research Articles

Tracking Minority Species in Redox Reactions: A Quantitative Combined XAS and Modulation Excitation Study.

Understanding the nature of intermediates/active species in reactions is a major challenge in chemistry. This is because spectator species typically dominate the experimentally derived data and consequently active phase contributions are masked. Transient methods offer a means to bypass this difficulty. In particular, modulation excitation with phase-sensitive detection (ME-PSD) provides a mechanism to distinguish between spectator and reacting species. Herein, modulation excitation (ME) time-resolved (energy dispersive) X-ray absorption spectroscopy, assisted by phase sensitive detection (PSD) analysis, has been applied to the study of a liquid phase process; in this case the classic ferrocyanide/ferricyanide redox couple. Periodic switches of the electrical potential (anodic/cathodic) enabled the use of the ME approach. Structural changes at fractions as low as 2 % of the total number of electroactive species were detected within the X-ray beam probe volume containing ~30 pmol of Fe(II)/Fe(III).

Tracking Minority Species in Redox Reactions: A Quantitative Combined XAS and Modulation Excitation Study

AbstractUnderstanding the nature of intermediates/active species in reactions is a major challenge in chemistry. This is because spectator species typically dominate the experimentally derived data and consequently active phase contributions are masked. Transient methods offer a means to bypass this difficulty. In particular, modulation excitation with phase‐sensitive detection (ME‐PSD) provides a mechanism to distinguish between spectator and reacting species. Herein, modulation excitation (ME) time‐resolved (energy dispersive) X‐ray absorption spectroscopy, assisted by phase sensitive detection (PSD) analysis, has been applied to the study of a liquid phase process; in this case the classic ferrocyanide/ferricyanide redox couple. Periodic switches of the electrical potential (anodic/cathodic) enabled the use of the ME approach. Structural changes at fractions as low as 2 % of the total number of electroactive species were detected within the X‐ray beam probe volume containing ~30 pmol of Fe(II)/Fe(III).

Influences of lidar scanning parameters on wind turbine wake retrievals in complex terrain

Abstract. Scanning lidars enable the collection of spatially distributed measurements of turbine wakes and the estimation of wake properties such as magnitude, extent, and trajectory. Lidar-based characterizations, however, may be subject to distortions due to the observational system. Distortions can arise from the resolution of the measurement points across the wake, the projection of the winds onto the beam, averaging along the beam probe volume, and intervening evolution of the flow over the scan duration. Using a large-eddy simulation and simulated measurements with a virtual lidar model, we assess how scanning lidar systems may influence the properties of the retrieved wake using a case study from the Perdigão campaign. We consider three lidars performing range-height indicator sweeps in complex terrain, based on the deployments of lidars from the Danish Technical University (DTU) and German Aerospace Center (DLR) at the Perdigão site. The unwaked flow, measured by the DTU lidar, is well-captured by the lidar, even without combining data into a multi-lidar retrieval. The two DLR lidars measure a waked transect from different downwind vantage points. In the region of the wake, the observation system reacts to the smaller spatial and temporal variations of the winds, allowing more significant observation distortions to arise. While the measurements largely capture the wake structure and trajectory over its 4–5 D extent, limited spatial resolution of measurement points and volume averaging lead to a quicker loss of the two lobes in the near wake, smearing of the vertical bounds of the wake (< 30 m), wake center displacements up to 10 m, and dampening of the maximum velocity deficit by up to a third. The virtual lidar tool, coupled with simulations, provides a means for assessing measurement capabilities in advance of measurement campaigns.

Infrared Spectroscopy of Live Cells Using High-Aspect-Ratio Metal-on-Dielectric Metasurfaces.

Fourier transform infrared (FTIR) spectroscopy is widely used for molecular analysis. However, for the materials situated in an aqueous environment, a precondition for live biological objects such as cells, transmission-based FTIR is prevented by strong water absorption of mid-infrared (MIR) light. Reflection-based cellular assays using internal reflection elements (IREs) such as high-index prisms or flat plasmonic metasurfaces mitigate these issues but suffer from a shallow probing volume localized near the plasma membrane. Inspired by the recent introduction of high-aspect-ratio nanostructures as a novel platform for manipulating cellular behavior, we demonstrate that the integration of plasmonic metasurfaces with tall dielectric nanostructures dramatically enhances the sensing capabilities of FTIR spectroscopy. We also demonstrate the ability of a metal-on-dielectric metasurface to transduce intracellular processes, such as protein translocation to high-curvature membrane regions during cell adhesion, into interpretable spectral signatures of the reflected light.

Measuring Transverse Relaxation with a Single-Beam 894 nm VCSEL for Cs-Xe NMR Gyroscope Miniaturization.

The spin-exchange-pumped nuclear magnetic resonance gyroscope (NMRG) is a pivotal tool in quantum navigation. The transverse relaxation of atoms critically impacts the NMRG's performance parameters and is essential for judging normal operation. Conventional methods for measuring transverse relaxation typically use dual beams, which involves complex optical path and frequency stabilization systems, thereby complicating miniaturization and integration. This paper proposes a method to construct a 133Cs parametric resonance magnetometer using a single-beam vertical-cavity surface-emitting laser (VCSEL) to measure the transverse relaxation of 129Xe and 131Xe. Based on this method, the volume of the gyroscope probe is significantly reduced to 50 cm3. Experimental results demonstrate that the constructed Cs-Xe NMRG can achieve a transverse relaxation time (T2) of 8.1 s under static conditions. Within the cell temperature range of 70 °C to 110 °C, T2 decreases with increasing temperature, while the signal amplitude inversely increases. The research lays the foundation for continuous measurement operations of miniaturized NMRGs.

Flight Testing Of A Single Point Frequency Sweeping Filtered Rayleigh Scattering Probe

"We present a successful in-flight application of filtered Rayleigh scattering (FRS) for temperature measurement in close proximity to the air plane using a newly developed single point, frequency sweeping probe. The temperature measurement is of relevance in the quantification of the density required for the evaluation of velocity from Pitot-probe measurements to obtain the true air speed (TAS). Laser optical air data sensors have the potential for contactless measurements outside the aerodynamic boundary layer. They are capable of self-diagnosis of fault conditions (e.g. signal loss, increased measurement uncertainty or spectral distortion for FRS) thereby increasing the safety of the aircraft. Compared to classical probes, they are less susceptible potential icing and blockage issues. The FRS-results presented here, are the outcome of two separate flight campaigns, carried out in the Alpine region as well as in the North Sea area. Measurement data provided information on the functionality of the FRS-system under various flight and weather conditions. Furthermore, the implementation of the FRS measurement system in the aircraft is presented; application aspects and improvements are discussed. In particular, the measurement accuracy at the actually achievable measurement rate was analyzed. For straight ahead flights at constant height, temperature mean values were in good agreement with the flight data system of the DLR research aircraft Dassault Falcon 20 (D-CMET). Aiming at in-flight air data measurements, the optical FRS measurement system requires a real-time temperature sample rate of a few Hz. We demonstrate that 2 FRS spectra per second can be acquired by a newly developed method using frequency sweeps for temperature determination. The low signal intensity of cw-laser based FRS is countered using a combined transmitter/receiver optic that focusses the entire cw-laser power into one measuring point. The light backscattered from the probe volume is collected by the same optics, filtered and imaged in a confocal arrangement onto a photomultiplier. An improved and miniaturized version of the presented FRS system could be a part of a future optical air data system (OADS). However, the strength of FRS signal relative to bright ambient conditions (e.g. sunlight, cloud backscatter) must be further improved in order to be able to measure well above cloud cover. The potential for further development is foreseen even if the accuracy required for flight data systems (~0.5 K) has not yet been achieved at a temperature measurement rate of 2 Hz. "

Dual-track spectrometer design for 1D gas-phase Raman spectroscopy

In this study, a new design for a 1D gas-phase Raman spectrometer is presented, utilizing two dedicated tracks to image different properties of the measured signal onto a single charge-coupled device (CCD) chip. Two possible configurations are shown: a polarization-separation configuration, which separates the detected Raman signal into s- and p-polarized shares; and a dual-resolution configuration, which captures all process-relevant species in a range of approximately 515-4650 cm−1 on one track and the highly resolved nitrogen spectrum on the other. This new spectrometer design offers several advantages when compared to traditional polarization-separation/dual-resolution systems, which often use switchable filters or two different spectrometers in tandem to achieve comparable measurements. Employing only one camera eliminates signal drift and minimizes calibration as well as spatial/spectral mapping issues. To validate instrument performance, the detection was paired with a continuous wave (CW) excitation system and used to measure in two generic but diagnostically challenging flow scenarios: flow near a heated surface, where thermal radiation is significant addressed by the polarization-separation configuration of the spectrometer and a channel flow at moderate temperatures in confined space, where the dual-resolution configuration of the spectrometer was employed. The results for both configurations and experiments showcase the instrument’s ability to effectively suppress background radiation (polarization-separation) or measure local gas-phase temperatures with higher accuracy (dual-resolution) and are complemented with resolution measurements yielding a maximum spatial resolution of 21.9 lp/mm along the 1D probe volume.

The lidar probe volume averaging effect: A wind tunnel investigation in streamwise turbulence with continuous-wave lidar

The main limitation of lidars to capture the turbulence is the filtering of small-scale fluctuations within the probe volume, which is far less significant with conventional anemometers. In this study, the probe volume averaging effect on the streamwise turbulence statistics is investigated in the wind tunnel. Different turbulent flows, which exhibit distinct turbulence intensities and integral length scales are generated and subsequently captured using a short-range continuous-wave WindScanner with different probe volumes. Hot wire measurements are performed as a reference. The results indicate that the turbulence intensity (TI) is underestimated using conventional lidar methods compared to the hot wire measurements. The relative error increases with the increasing ratio of probe volume over integral length scale (l p /L) which is the indication of probe volume averaging. The TI is underestimated by 4 % at l p /L = 0.5 and by 63 % at the largest tested l p /L = 11.3 with the conventional lidar method. However, the TI estimated from the averaged Doppler spectrum of the lidar compensates for the probe volume averaging effect and shows a better agreement with the hot wire measurements with an average overestimation of 7.8 %. This study shows that the continuous-wave lidars have the potential to estimate the TI under different flow conditions using the averaged Doppler spectrum method.

Absorption Correction for 3D Elemental Distributions of Dental Composite Materials Using Laboratory Confocal Micro-X-ray Fluorescence Spectroscopy.

Confocal micro-X-ray fluorescence (micro-XRF) spectroscopy facilitates three-dimensional (3D) elemental imaging of heterogeneous samples in the micrometer range. Laboratory setups using X-ray tube excitation render the method accessible for diverse research fields but interpretation of results and quantification remain challenging. The attenuation of X-rays in composites depends on the photon energy as well as on the composition and density of the material. For confocal micro-XRF, attenuation severely impacts elemental distribution information, as the signal from deeper layers is distorted by superficial layers. Absorption correction and quantification of fluorescence measurements in heterogeneous composite samples have so far not been reported. Here, an absorption correction approach for confocal micro-XRF combining density information from microcomputed tomography (micro-CT) data with laboratory X-ray absorption spectroscopy (XAS) and synchrotron transmission measurements is presented. The energy dependency of the probing volume is considered during the correction. The methodology is demonstrated on a model composite sample consisting of a bovine tooth with a clinically used restoration material.

Temporally modulating laser pulses to stabilize LIBS measurement locations under large gas temperature gradients

In combustion research, laser-induced breakdown spectroscopy (LIBS) has been widely employed in local equivalence ratio measurement. However, the potential temperature gradients in the probe volume can significantly affect the shape of induced plasmas, resulting in unstable measurement locations. In this work, we improved the stability of measurement locations by modulating the laser pulse duration. In a hot-cold gas flow interface with large temperature gradients, when using the original laser pulse with a full width at half maximum (FWHM) of 4 ns, the locations of initial plasma core were insensitive to gradient variations; however, the plasma expansion behaviors differed significantly after 3 ns. The hot spots of plasmas diverged bi-directionally under high temperature, resulting in two-lobe structures and unstable measurement locations. After the laser pulse was modulated to a shorter duration using a pressure chamber, the plasma expansion was suppressed which constrained the plasma volume. Specifically, using a modulated pulse with a FWHM of 1.9 ns, the two-lobe structure was eliminated across the interface, and the standard deviation of measurement locations was reduced to 0.27 mm. The measured equivalence ratios across the interface showed favorable agreement with the simulation.

A new coaxial flow-through probe for electromembrane extraction of methadone from clinical samples on-line coupled to capillary electrophoresis

BackgroundA new design of a flow-through coaxial electromembrane extraction (EME) probe that can be on-line coupled with CE instrument is described and tested. The supporting base of the probe is a PDMS microchip with T-shaped channels into which two coaxially arranged capillaries for inlet and outlet solutions are inserted. The extraction part of the probe is a porous polypropylene hollow fiber, sealed at one end and modified with nitrophenyloctyl ether (NPOE) extraction fluid. The internal volume of the extraction probe is 1.1 μL. ResultsThe EME probe was tested on laboratory samples and methadone was extracted into 3.0 M AcOH as acceptor. The concentration dependence was linear in the range of 0.1–1.0 μg mL−1 at EME 300 s/150 V and in the range of 0.5–10.0 μg mL−1 at EME 100 s/150 V. The enrichment factor was greater than 30 and the LOD was 0.21 μg mL−1. The EME of methadone in clinical samples showed a linear concentration dependence in human urine and a nonlinear concentration dependence in serum. The distribution of methadone in each phase of the extraction system and the effect of extraction membrane thickness on the enrichment factor were studied. The EME probe can be applied repeatedly. SignificanceThe supporting base of EME probe and flow gating interface (FGI) are realized by a microfluidic PDMS microchips cast in the laboratory without the use of lithography. A supporting PDMS chip with coaxially arranged capillaries and extraction membrane forms a compact analytical instrument. The entire EME/CE analysis process is performed on a laboratory-made instrument and automated by LabView.

Establishment of a rapid counting method for lactic acid bacteria and yeast in dairy products

The plate count agar (PCA) method is a common technique used to count microorganisms in dairy products, but this method is time‐consuming and highly selective by the medium. This study adopted Lab158 and PF2 as the universal probes for hybridising lactic acid bacteria and yeasts, respectively, and investigated the effects of fixation time, hybridisation time, hybridisation temperature, probe concentration and propidium iodide (PI) concentration on hybridisation efficiency in the samples. The results showed that the highest hybridisation efficiency for lactic acid bacteria and yeast, along with the best double staining results, was observed under the following conditions: a fixation time of 80 min, a hybridisation time of 180 min, a hybridisation temperature of 48°C, a probe volume of 5 μL for lactic acid bacteria and 3 μL for yeast, and a PI volume of 5 μL for lactic acid bacteria and 3 μL for yeast. The fluorescence in situ hybridisation‐flow cytometry (FISH‐FCM) and PCA counting results showed a significant positive correlation (r > 0.9). The FISH‐FCM and PCA counting results showed a significant positive correlation (r > 0.9). The FISH‐FCM counting method can serve as a quick and accurate method for the counting of lactic acid bacteria and yeast in dairy products.

Brain microstructure and connectivity in COVID-19 patients with olfactory or cognitive impairment

IntroductionThe COVID-19 pandemic has affected millions worldwide, causing mortality and multi-organ morbidity. Neurological complications have been recognized. This study aimed to assess brain structural, microstructural, and connectivity alterations in patients with COVID-19-related olfactory or cognitive impairment using post-acute (time from onset: 264[208–313] days) multi-directional diffusion-weighted MRI (DW-MRI). MethodsThe study included 16 COVID-19 patients with cognitive impairment (COVID-CM), 35 COVID-19 patients with olfactory disorder (COVID-OD), and 14 controls. A state-of-the-art processing pipeline was developed for DW-MRI pre-processing, mean diffusivity and fractional anisotropy computation, fiber density and cross-section analysis, and tractography of white-matter bundles. Brain parcellation required for probing network connectivity, region-specific microstructure and volume, and cortical thickness was based on T1-weighted scans and anatomical atlases. ResultsCompared to controls, COVID-CM patients showed overall gray matter atrophy (age and sex corrected p = 0.004), and both COVID-19 patient groups showed regional atrophy and cortical thinning. Both groups presented an increase in gray matter mean diffusivity (corrected p = 0.001), decrease in white matter fiber density and cross-section (corrected p < 0.05), , and COVID-CM patients also displayed an overall increased diffusivity (p = 0.022) and decreased anisotropy (corrected p = 0.038) in white matter. Graph-based analysis revealed reduced network modularity, with an extensive pattern of connectivity increase, in conjunction with a localized reduction in a few connections, mainly located in the left hemisphere. The left cingulate, anterior cingulate, and insula were primarily involved. ConclusionExpanding upon previous findings, this study further investigated significant alterations in brain morphology, microstructure, and connectivity in COVID-19 patients with olfactory or cognitive disfunction. These findings suggest underlying neurodegeneration, neuroinflammation, and concomitant compensatory mechanisms. Future longitudinal studies are required to monitor the alterations over time and assess their transient or permanent nature.

A sensitive lateral flow immunoassay relying on time-resolved fluorescent microspheres immune probe for determination of ceftiofur and its metabolite

Ceftiofur (CEF) is an antimicrobial agent with high efficiency and low toxicity, desfuroylceftiofur is its main metabolite, but they are also have potential harm to human health. In this study, ceftiofur was combined with carrier proteins to get artificial antigens. A specific antibody (pAb) against CEF and desfuroylceftiofur was prepared. A sensitive and rapid paper-based sensor relying on time-resolved fluorescent microspheres (TRFMs) immune probes was developed, which were time-resolved fluorescent immunochromatographic strips (TRFMs-LFIA). The concentrations of T line and C line, activated pH, antibody volume and probe volume were optimized. Quantitative limits of detection (qLODs) of TRFMs-LFIA for CEF and desfuroylceftiofur were 0.97 ng/mL and 0.41 ng/mL, respectively. And 50 % inhibiting concentrations (IC50) were 12.92 ng/mL and 12.58 ng/mL, respectively. Pretreatment procedures of real samples were simple and rapid. Detection time of TRFMs-LFIA strip was 15 min. Qualitative analysis of CEF and desfuroylceftiofur was achieved under a UV light, quantitative analysis was implemented with a fluorescent immunoassay analyzer. The average recovery rates ranged from 91.4 % to 107.7 % and corresponding coefficients of variation (CV) was 1.5%–9.7 %. Concentration levels of artificially-spiked samples were measured by TRFMs-LFIA and compared with detection results of High performance liquid chromatography (HPLC), which showed a good accordance. These results indicated that the proposed assay can provide an effective strategy for on-site detection of CEF and desfuroylceftiofur simultaneously.

(Invited) Confocal Raman Microscopy in the Study of Ion Insertion Processes and Material Dimensional Change

Confocal Raman microscopy is being applied to quantify chemical composition at electrode-solution interfaces and within electrode-supported films under electrochemical potential control. Experimental strategies (i.e., cell designs and data acquisition and processing techniques) that are enabling sensitive in-situ spectral measurements will be discussed with focus on redox transformations at electrode-solution interfaces and within electrode-supported polymer membranes and thin films. Emphasis will be on the ability to investigate ion insertion/de-insertion processes and measure material dimensional (e.g., swelling/de-swelling) changes as the applied potential is varied (in-situ). The microscope system being utilized employs a high numerical aperture oil immersion objective to achieve (i) diffraction-limited focusing and probe volume characteristics and (ii) high efficiency in collecting Raman scattered radiation from molecules of interest. With the objective mounted to an inverted microscope frame, the electrochemical cell is positioned above the objective on the microscope stage. A glass microscope coverslip attached to the bottom of the electrochemical cell serves as the optical window. One electrochemical cell platform has been constructed around an optically transparent indium tin oxide (ITO) coated coverslip that serves as both the cell working electrode and optical window. The objective brings excitation radiation through the coverslip and to a focus a few micrometers above the ITO surface. Species diffusing into the confocal probe volume region are detected and quantified based on their Raman spectral band frequencies and intensities. A second electrochemical cell platform has a thin layer design and enables use of conventional disk working electrodes. The performance of this cell together with a spectral difference technique that allows detection of transformations within redox polymers supported on carbon electrodes will be discussed. The platform is being applied to detect swelling/de-swelling in electrode-supported redox polymers in response to changes in material redox state. Molecular composition (i.e., the mix of polymer framework, solvent and mobile ions) within the confocal probe volume is measured quantitatively from Raman spectra. Tracking the frequency and intensity of spectral bands as electrode potential is varied enables voltage-induced swelling and de-swelling to be correlated to changes in the composition of specific types of mobile species (solvent and ions). Similar application of the strategy to investigate material dimensional change with variation in atmospheric composition will be highlighted.

Technical comparison of Abbott’s UroVysion® and Biocare’s CytoFISH urine fluorescence in situ hybridization (FISH) assays

BackgroundThis study aims to compare the technical performance of Abbott’s UroVysion and Biocare’s CytoFISH urine cytology probe panel and position the CytoFISH probe panel as an alternative to UroVysion. The CytoFISH probe panel was developed based on clinically sensitive chromosomes found to be amplified in bladder cancers, as well as a locus-specific probe also seen to be amplified in bladder tumors. After extensive testing comparing CytoFISH to UroVysion, we present here our findings for the two assays.Materials and methodsA total of 216 cases representing a mix of male (ages 36–99) and female (ages 46–91) patients were assayed with both probe sets. The CytoFISH and UroVysion probe panels were tested in accordance with the UroVysion procedure, as outlined in the manufacturer’s supplied package insert with the following exception: the probe volume used was 3µL for UroVysion and 5µL for CytoFISH.ResultsThe scoring used for the CytoFISH and UroVysion assays revealed a 95% concordance, suggesting that Biocare’s CytoFISH Test has at least the same clinical sensitivity and specificity as claimed by the Abbott UroVysion Kit. We found that the CytoFISH 5p15.2 locus-specific probe was easier to score than UroVysion’s 9p21 deletion.ConclusionThe high rate of concordance between the two assays suggests that Biocare’s CytoFISH assay is a robust alternative to Abbott’s UroVysion in the diagnosis and monitoring of bladder carcinoma.

Mechanical cycling-induced evolution of structure and local mechanical properties in a PdCuNiP bulk metallic glass

To improve the ductility of bulk metallic glasses (BMGs), external mechanical stimulations can be applied. Thereby, cyclically loading the samples at stress levels below the macroscopic elastic limit leads to permanent structural changes, which can alter the plasticity in bulk metallic glasses. Here, the effect of systematic variations of Pd43Cu27Ni10P20 BMG's structural state, achieved through cyclically loading the material to 70, 80, and 90% of the yield strength, on a range of mechanical properties like modulus, hardness, yield strength, strain rate sensitivity, activation volume, maximum shear stress and stiffness at different probing volume is studied. It is observed that samples rejuvenated from the non-cycled state to the 70% of yield stress state, relaxed when cycled up to 80% of yield stress, and finally rejuvenated again when cycled up to 90% of yield stress. This rejuvenation to relaxation transition might be due to the random atomic rearrangement during the cycling.

Impact of probe volume and peak detection methods on lidar rotor effective wind speed and turbulence intensity estimations

Lidar simulation techniques are a suitable and increasingly reliable alternative for testing lidar measuring strategies and illustrating their response when combined with modelled wind fields. In this work, two simulation tools are combined to assess the uncertainty in the derivation of the rotor effective wind speed and the wind speed variance from a forward-looking nacelle-mounted continuous wave lidar wind speed estimations. These uncertainties are analysed for a variety of atmospheric turbulence levels and lidar measuring strategies. A synthetic turbulence generator is used to create the reference wind fields. Subsequently, a lidar simulator operated in a continuous-wave mode is used to scan the synthetic wind fields and perform a sensitivity analysis by comparing first- and second-order statistics against reference values. The lidar simulator is enhanced with three Doppler peak detection methods, namely the maximum, the median and the centroid, to extract radial wind speeds from the velocities found within the probe volume. The results show that probe volume and peak detection methods influence the uncertainty of the wind speed variance. The uncertainty in time-averaged and instantaneous rotor effective wind speed estimations is not sensitive to the lidar spatial averaging or peak detection methods investigated. Finally, we saw that the turbulence intensity influences the derived lidar quantities and is the main driver of the variations in rotor effective wind speed uncertainty estimations.

Validity of Single Fluorescent Molecule to Report Local Dynamics of a Polymer Matrix: The Effect of Molecular Architecture

AbstractThe influence of van der Waals volume as well as molecular configuration of the probe on its rotation is investigated by defocused single molecule fluorescence microscopy. The results show that the probe with a larger van der Waals volume has lower integrated power spectra density and the fraction of rotational molecules at each temperature. However, the asymmetric configuration of probe can make the integrated power spectra density and the fraction of rotational molecules larger. Therefore, the van der Waals volume of probe is the most dominating factor to determine the length scales and frequency of reported local dynamics while the asymmetric configuration of probe can bring about additional effect.

Ultrasensitive Detection and Separation of Pancreatic Cancer Biomarker CA 19-9 Using a Multiphoton Laser Wave-Mixing Detector Interfaced to Capillary Electrophoresis.

The carbohydrate antigen 19-9 (CA 19-9) is the most commonly used biomarker in the clinical diagnosis of pancreatic cancer. Multiphoton nonlinear laser wave-mixing spectroscopy is presented as an ultrasensitive detection method for CA 19-9. Wave mixing is an optical absorption-based method, and hence, one can detect CA 19-9 without labels in their native form using compact ultraviolet (UV) lasers or labeled samples using a visible laser. The wave-mixing signal exhibits a quadratic dependence on the sample concentration, and hence, it is an ideal sensor to monitor small changes in the sample. Wave mixing has inherent advantages over other absorption-based detection methods, including short optical path length (micrometer-thin samples instead of 1 cm cuvette) and excellent spatial resolution (micrometer probe). Since the laser wave-mixing probe volume is small (picoliter), it is convenient to interface to microfluidics or capillary-based electrophoresis systems to enhance chemical specificity. Our wave-mixing detectors could be configured as portable battery-powered devices suitable for field use. Laser wave-mixing spectroscopy offers enhanced selectivity levels for protein detection when coupled with capillary electrophoresis (CE). We report a concentration detection limit of 0.16 U/mL, and a corresponding mass detection limit of 1.2 × 10-8 U, and these detection limits are better than those of chemiluminescence- or ELISA- based methods.