Capillary blood collected by finger-prick in the form of dry blood spots (DBS) might be ideal for POC as patients can perform sample collection by themselves at home and requirements for transportation of the DBS samples are minimal. The most frequently reported technologies for detection of DBS samples include ELISA, high-pressure liquid chromatography (HPLC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS).
Two main concerns have made this practice difficult so far: (i) bursting of red blood cells after whole blood is dried, which can result in higher non-specific interaction between the ruptured cell fragments and the sensor surface and (ii) altered structure of analytes due to the drying process, which can influence the efficiency of the analytes entering the extraction buffer and induce increased variation of the extraction efficiency.
The capacity of the FOx Biosystems POC FO-SPR bioassay was assessed using DBS samples. Following the optimized protocol for DBS sample preparation, 98 % of extraction efficiency was calculated for IFX, suggesting that :
(i) the drying process of blood did not affect the extraction of IFX or its interaction with the antibodies used in the FO-SPR bioassay,
(ii) the distribution of IFX on the DBS paper was uniform given that only part of the paper was used for extraction process and
(iii) non-specific binding (due to the bursting of blood cells caused by drying of whole blood) was not interfering with the FO-SPR bioassay.
The obtained LOD values were below 2 ng/mL, irrespective of whether IFX was spiked in the whole blood prior or after the extraction.
The FOX technology allows to directly measure the analyte of interest, irrespective of the matrix type. This allows to directly calculate the actual extraction efficiencies without significant differences in the calibration curve behavior. This application demonstrates the versatility and robustness of the FO-SPR biosensor that can be used as a central laboratory diagnostic tool or even as a POC device.