Microsampling with cotton thread: Storage and ultra-sensitive analysis by thread spray mass Spectrometry

Abstract

Storage and quantitative analysis of small volumes of biofluids are challenging, especially when low concentrations of analytes are to be detected in the presence of complex matrices. In this study, we describe an integrated thread-based approach for stabilizing small blood volumes in the dry-state at room temperature, while also offering direct analysis capabilities via thread spray mass spectrometry. The analytical merits of this novel microsampling platform was demonstrated via the direct analysis of diazepam and cocaine in dried blood samples stored for 42 days. In-situ in-capillary blood processing from hydrophobic threads enabled limits of detection as low as parts-per-quadrillion to be reached. We validated this ultra-sensitivity by analyzing small tissue-like residues collected after pushing a thread through the sample once. The implications of this sample collection, storage, and analysis platform can be extensive with direct applications in forensics and clinical studies.

Keywords: Analytical methods; Dried blood storage; Mass spectrometry; Microsampling; Thread spray.

Figure 1.

A) SEM image of untreated cotton thread and schematic of silane functionalization for hydrophobic surface modification. B) Hydrophobic thread spray setup, a single piece of thread with pre-deposited sample is placed in a glass capillary and a suitable solvent applied. The inset shows Taylor cone formation, after application of onset voltage (3 kV).

Figure 2.

A) Benzoylecgonine ion yield as a function of extraction time after drying analyte onto various threads types: untreated, 30- and 60-min treated substrates. B) Average ion intensity is recorded as a function of blood volume for cocaine deposited on 60-minute treated thread. Calibration curves for diazepam in the concentration range of C) 0.2 – 100 ng/mL and D) 0.2 – 100 pg/mL in 10 μL dried whole blood on untreated and 60-minute treated cotton threads, respectively. Error bars indicate standard deviation for five replicates.

Figure 3.

Stability profiles of A) diazepam and B) cocaine in 10 μL dried whole blood on untreated, 30 minutes treated, and 60 minutes treated thread substrates stored over a six-week period under ambient conditions. Error bars represent five replicates.

Figure 4.

A) Photograph showing a viable tissue-mimicking agarose bead soaked with McCoy’s 5A media with 10% FBS and L-glutamine. Tissues sampling occurred via 60 minutes treated thread suspended on a needle. B) Concentration dependence of diazepam in agarose beads. The ratio of diagnostic ions for diazepam and its isotopically-labelled species were plotted. Error bars represent three replicates. C) Stability profile of agarose beads infused with 250 ng/mL diazepam over a four-week period. Error bars represent five replicates. D) Representative tandem MS spectrum of 100 ng/mL diazepam doped agarose bead sample.