A novel sampling concept for mass spectrometric bottom-up targeted protein analysis is here demonstrated with polymeric sampling spots integrated with instant immunocapture for analysis of dried matrix spots. The polymers 2-hydroxyethyl methacrylate-co-2-vinyl-4,4-dimethyl azlactone (pHEMA-VDM) and pHEMA-Tosyl for covalent attachment of antibodies where investigated alongside with adsorption on non-treated filter paper. From performance characterization, the pHEMA-VDM had the best performance. The sampling spots demonstrated fast and easy sampling and preparation of human serum spiked with the biomarker human chorionic gonadotropin. The sampling spots enabled a detection limit of 1 ng/mL (26.4 pM) within a five point concentration curve from 1 ng/mL to 20 ng/mL (R2 = 0.97). The detection limit was demonstrated to be two times lower than previously demonstrated with standard DMPK-C sampling cards. A five point concentration curve from 100 ng/mL to 2000 ng/mL was also investigated (R2 = 0.998). Intra day precision was within 16% and 23% for concentration range 1 ng/mL to 20 ng/mL and 100 ng/mL to 2000 ng/mL, respectively. Inter day precision was within 20%. Accuracy was determined to 10% and 11% for 2.5 ng/mL and 20 ng/mL, respectively. The sampling spots were also demonstrated in a realistic setting where serum samples from two confirmed patients with testicular germ cell cancer were analyzed. These analyses confirmed an elevated hCG content in the sera of 418.5 ± 4.2 ng/mL and 21 ± 0.02 ng/mL hCG for patient one and two respectively.
Keywords: Bottom-up protein analysis; Dried matrix spots; Mass spectrometry; On-paper immunocapture; Smart-sampling.
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