Microfluidic-based volumetric sampling as a haematocrit-independent DBS collection strategy

Central nervous system (CNS) drugs require accurate therapeutic drug monitoring (TDM) in a combined bioanalytical and clinical approach. TDM is performed in order to evaluate the suitability of prescribed therapies by measuring drug plasma concentrations to optimise dose regimen, minimise toxicity and for overall clinical decision-making. For this purpose, the use of microsampling, namely dried blood spots (DBS), involves considerable advantages compared to the classic in-tube plasma analysis approach, both for clinicians and patients: in fact, a minimally invasive sample collection allows more frequent and accurate monitoring. These advantages are in addition to those related to simplified handling and storage, fast processing and feasible analysis procedures. On the other hand, quali-quantitative results obtained by the DBS approach can be affected by volumetric bias due to blood haematocrit (HCT) and density, reflecting on spot size and homogeneity, sampling reproducibility, accuracy and precision of analytical data. For this reason, in-depth studies have been carried out in order to investigate the correlations between HCT values and DBS analysis results. To overcome HCT-dependent bias, an alternative strategy based on microfluidic devices has been proposed: a fixed, small volume (5-10 µL) of whole blood is accurately collected in a microfluidic channel-based device to generate DBS samples regardless of blood viscosity. As a proof of concept, this innovative approach was designed and developed on aripiprazole, an atypical antipsychotic used in the treatment of schizophrenia and bipolar disorder. To this aim, an original analytical methodology was developed, validated and successfully applied for the analysis of DBS samples obtained by microfluidic devices from patients undergoing aripiprazole treatment. The resulting data has shown the novel microfluidic-based microsampling procedure grants accurate and precise results, irrespective of HCT. This research work provides an effective strategy based on microcapillaries to collect a fixed small volume of whole blood, which could overcome HCT biases in DBS and promises to be feasible and reliable while maintaining all the advantages of classic DBS analysis, making it suitable for widespread bioanalytical applications.