Validation of high-throughput, semiquantitative solid-phase SARS coronavirus-2 serology assays in serum and dried blood spot matrices.

Aim: Serological assays for the detection of anti-SARS coronavirus-2 (SARS-CoV-2) antibodies are essential to the response to the global pandemic. A ligand binding-based serological assay was validated for the semiquantitative detection of IgG, IgM, IgA and neutralizing antibodies (nAb) against SARS-CoV-2 in serum. Results: The assay demonstrated high levels of diagnostic specificity and sensitivity (85-99% for all analytes). Serum IgG, IgM, IgA and nAb correlated positively (R2 = 0.937, R2 = 0.839, R2 = 0.939 and R2 = 0.501, p < 0.001, respectively) with those measured in dried blood spot samples collected using the hemaPEN® microsampling device (Trajan Scientific and Medical, Victoria, Australia). In vitro SARS-CoV-2 pseudotype neutralization correlated positively with the solid phase nAb signals in convalescent donors (R2 = 0.458, p < 0.05). Conclusion: The assay is applicable in efficacy studies, infection monitoring and postmarketing surveillance following vaccine rollout.

In vitro testing of the hemaPEN microsampling device for the quantification of acetaminophen in human blood.

Background: The hemaPEN is a liquid microsampling device for the reproducible collection and storage of blood samples as dried blood spots, for subsequent quantitative analysis. Materials & methods: We examined the device's ability to collect accurate and precise blood volumes, at different hematocrit levels, via in vitro studies using acetaminophen in human blood. We also investigated the impact of different user training approaches on device performance. Results: The hemaPEN demonstrated acceptable volumetric accuracy and precision, regardless of the training medium used. Issues with apparent hematocrit-dependent bias were found to be associated with the extraction process, rather than the volumetric performance of the device. Conclusion: The hemaPEN is capable of readily producing high quality blood microsamples for reproducible and accurate quantitative bioanalysis.

Correction to: Precise, accurate and user-independent blood collection system for dried blood spot sample preparation.

The authors would like to call the reader's attention to the following: The instrument they used to measure the volumetric precision of the dispensing devices is not called "VMS" but "PCS®".

Precise, accurate and user-independent blood collection system for dried blood spot sample preparation.

An accurate and precise 3 µL blood collection and dispensing system is presented for the preparation of dried blood spot (DBS) samples. Using end-to-end glass capillaries in conjugation with pre-punched DBS pads, a blood micro collection system was developed to eliminate the haematocrit dispersion, widely associated with DBS technology, while providing better levels of accuracy and precision during sample preparation. This methodology is compared to traditional micro-volume blood collection systems, such as a pipette and a digitally controlled analytical syringe. Results showed that % of recovery for the capillary methodology was closer to 100% across the three haematocrit (HCT) levels tested and when prepared by two users (98 to 100% for capillaries, 78 to 104% for pipette and 93 to 97% for digital syringe) attesting a higher accuracy. Additionally, by taking advantage of the capillary action mechanism to collect and dispense autonomously the desired volume of blood onto the DBS pad, coefficients of variation between two individuals were significantly lower than with standard methodologies (capillaries-0.05 to 0.77%, pipette-12.71 to 18.53% and digital syringe-0.72 to 1.77%). This alternate aspiration and dispensing methodology could be used by different users without compromising accuracy or precision when handling low volumes of blood during the pre-analytical steps. Graphical abstract Comparison of novel capillary dispensing methodology for dried blood spot sample preparation with pipette and digital syringe methodologies through accuracy and precision measurements of caffeine.

Principles around Accurate Blood Volume Collection Using Capillary Action.

Capillary action is one mechanism microfluidics uses to draw liquid autonomously in a substrate without the need of external energy. This behavior can be exploited to collect accurate volumes of liquids such as blood in narrow columns known as capillary tubes and help the development of inexpensive, user-friendly personalized biomedical tools. Precision bore glass capillaries demonstrate the "state of the art" for volume accuracy and precision, but height and radius must be carefully chosen in order to exploit the capillary action behavior efficiently. This Article investigates the influence of surface glass aging, due to prolonged exposure to humid air, and hematocrit level on the blood capillary rise. It provides also the tools to correctly define the optimum capillary dimensions to collect an accurate volume of blood in a glass capillary tube.

A rapid assay for Hendra virus IgG antibody detection and its titre estimation using magnetic nanoparticles and phycoerythrin.

Detection of Hendra viral IgG antibody in animal sera is useful for surveillance following a virus outbreak. The commonly used enzyme-linked immunosorbent assay and fluorescence-based Luminex assay typically consist of three steps and take at least several hours to complete. We have simplified the procedure to two steps in an effort to develop a rapid procedure for IgG antibody, but not IgM antibody, detection. This is achieved by conjugating the fluorescence label R-phycoerythrin directly onto the IgG binding protein Protein G. The use of magnetic nanoparticles, due to their large specific surface area, has helped reduce each of the binding steps to 20 min. As a result, the whole assay can be completed in 60 min. We also demonstrate a method to quickly estimate IgG antibody titres by assaying the sera at only two dilutions (i.e. 1:20 and 1:1000) and using the fluorescence ratio at these dilutions as an indicator of antibody titre. The results of this approach correlated well with the well-regarded serum neutralization test in virus antibody assays. This protocol reported here can be adopted in Luminex assays, fluorescence-linked immunosorbent assays and assays on microfluidics platforms for rapid antibody surveillance of Hendra and other viruses.

Versatile SERS sensing based on black silicon.

Black Si (b-Si) with gold or silver metal coating has been shown to be an extremely effective substrate for surface-enhanced Raman scattering (SERS). Here, we demonstrate that it is also a highly versatile SERS platform, as it supports a wide range of surface functionalizations. In particular, we report the use of a molecularly imprinted polymer (MIP) coating and a hydrophobic coating on b-Si to establish two different sensing modalities. First, using a MIP layer on Au-coated b-Si, we show selective sensing of two closely related varieties of tetracycline. Second, a hydrophobic coating was used to concentrate the analyte adsorbed on gold colloidal nanoparticles, thus increasing the sensitivity of the measurement by an order of magnitude. In this experiment, Au nanoparticles and analyte were mixed just before SERS measurements and were concentrated by drop-drying on the super-hydrophobic b-Si. These approaches are promising for SERS measurements that are sensitive to the aging of bare plasmonic metal-coated substrates.

Split and flow: reconfigurable capillary connection for digital microfluidic devices.

Supplying liquid to droplet-based microfluidic microsystems remains a delicate task facing the problems of coupling continuous to digital or macro- to microfluidic systems. Here, we take advantage of superhydrophobic microgrids to address this problem. Insertion of a capillary tube inside a microgrid aperture leads to a simple and reconfigurable droplet generation setup.

Electro-(de)wetting on superhydrophobic surfaces.

Usually, electrowetting on superhydrophobic surfaces (EWOSS) is generated by application of an alternating current signal and often leads to droplet impalement into the structuration. To avoid this phenomenon, superhydrophobic surfaces must show robustness to high pressure. Otherwise, an external energy has to be applied to dewet the droplet from the structuration. We present, in this article, an original approach to actuate liquid droplets via a modulated EWOSS signal (MEWOSS). This technique allows the dewetting of the droplet due to periodic vibrations induced by the electrowetting actuation. In that case, it is possible to investigate a larger range of superhydrophobic surfaces under EWOSS without droplet impalement. Three different superhydrophobic surfaces, showing different degrees of impalement under EWOSS, are investigated and compared using this MEWOSS technique.

High sensitive matrix-free mass spectrometry analysis of peptides using silicon nanowires-based digital microfluidic device.

We present for the first time an electrowetting on dielectric (EWOD) microfluidic system coupled to a surface-assisted laser desorption-ionization (SALDI) silicon nanowire-based interface for mass spectrometry (MS) analysis of small biomolecules. Here, the transfer of analytes has been achieved on specific locations on the SALDI interface followed by their subsequent mass spectrometry analysis without the use of an organic matrix. To achieve this purpose, a device comprising a digital microfluidic system and a patterned superhydrophobic/superhydrophilic silicon nanowire interface was developed. The digital microfluidic system serves for the displacement of the droplets containing analytes, via an electrowetting actuation, inside the superhydrophilic patterns. The nanostructured silicon interface acts as an inorganic target for matrix-free laser desorption-ionization mass spectrometry analysis of the dried analytes. The proposed device can be easily used to realize several basic operations of a Lab-on-Chip such as analyte displacement and rinsing prior to MS analysis. We have demonstrated that the analysis of low molecular weight compounds (700 m/z) can be achieved with a very high sensitivity (down to 10 fmol µL(-1)).

Reversible electrowetting on superhydrophobic double-nanotextured surfaces.

The paper reports on wetting, electrowetting (EW), and systematic contact angle hysteresis measurements after electrowetting of superhydrophobic silicon nanowire surfaces (NWs). The surfaces consist of C4F8-coated silicon nanowires grown on Si/SiO2 substrate. Different surfaces modulating (i) the dielectric layer thickness and (ii) the nanotexturation were investigated in this study. It was found that the superhydrophobic NWs display different EW behaviors according to their double nanotexturation with varying droplet impalement levels. Some surfaces exhibited a total reversibility to EW with no impalement (contact angle variation of 35+/-2 degrees at 190 VTRMS with deionized water), whereas other surfaces showed nonreversible behavior to EW with partial droplet impalement. A scenario is proposed to explain the unique properties of these surfaces.