Whole-blood microsampling provides many benefits such as remote, patient-centric, and minimally invasive sampling. However, blood plasma, and not whole blood, is the prevailing matrix in clinical laboratory investigations. The challenge with plasma microsampling is to extract plasma volumes large enough to reliably detect low-concentration analytes from a small finger prick sample. Here we introduce a passive plasma filtration device that provides a high extraction yield of 65%, filtering 18 μL of plasma from 50 μL of undiluted human whole blood (hematocrit 45%) within less than 10 min. The enabling design element is a wedge-shaped connection between the blood filter and the hydrophilic bottom surface of a capillary channel. Using finger prick and venous blood samples from more than 10 healthy volunteers, we examined the filtration kinetics of the device over a hematocrit range of 35−55% and showed that 73 ± 8% of the total protein content was successfully recovered after filtration. The presented plasma filtration device tackles a major challenge toward patient-centric blood microsampling by providing highyield plasma filtration, potentially allowing reliable detection of low-concentration analytes from a blood microsample.

Obtaining plasma from a blood sample and preparing it for subsequent analysis is currently a laborious process involving experienced health-care professionals and centrifugation. We circumvent this by utilizing capillary forces and microfluidic engineering to develop an autonomous plasma sampling device that filters and stores an exact amount of plasma as a dried plasma spot (DPS) from a whole blood sample in less than 6 min. We tested 24 prototype devices with whole blood from 10 volunteers, various input volumes (40− 80 μL), and different hematocrit levels (39−45%). The resulting mean plasma volume, assessed gravimetrically, was 11.6 μL with a relative standard deviation similar to manual pipetting (3.0% vs 1.4%). LC-MS/MS analysis of caffeine concentrations in the generated DPS (12 duplicates) showed a strong correlation (R 2 = 0.99) to, but no equivalence with, concentrations prepared from corresponding plasma obtained by centrifugation. The presented autonomous DPS device may enable patient-centric plasma sampling through minimally invasive finger-pricking and allow generatation of volume-defined DPS for quantitative blood analysis.

A sensitive photoacoustic absorption spectrometer for highly transparent solids has been built and tested. As the light source an optical parametrical oscillator pumped by a nanosecond pulse laser with 10 Hz repetition rate is employed, covering the complete wavelength range from 407 to 2600 nm. A second-harmonic-generation unit extends the range of accessible wavelengths down to 212 nm. A lead-zirconate-titanate piezo transducer, directly coupled to the sample, detects the photoacoustically generated sound waves. Absorption spectra of lithium triborate, lithium niobate, and alpha barium borate crystals with absorption coefficients down to 10(-5) cm(-1) are presented.

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