Microsampling of proteins from biological matrices: sampling methods and devices, typical workflows, clinical...

In bioanalysis microsampling has evolved as a promising alternative to conventional blood sampling. This is also true for mass spectrometry-based protein analysis. Developments in sampling technology and liquid chromatography mass spectrometry the last 10-15 years have expanded the field from dried blood spots sampled on paper for newborn screening to a variety of sampling devices, and applications spanning from monitoring of low abundance biomarkers through therapeutic drug monitoring of biopharmaceuticals to anti-doping analysis and multi-omics. This review gives an overview of the resent progress (2021-2026) in liquid chromatography mass spectrometry-based protein analysis from dried microsamples. We start with comparing dried microsampling to conventional blood sampling. Then we describe the different dried microsampling devices and developments, and highlights applications from different biological matrices. The typical analytical protein workflow is covered with examples from recent literature. All steps from sample extraction, through bottom-up and top-down workflows to targeted and non-targeted analysis are described together with standardization methods and automation. A few recent clinical examples and novel applications are discussed in more detail. These cover therapeutic monoclonal antibody monitoring, multiplex biomarker determination, proteome profiling and multi-omics. We also present two recent innovations: dried blood immunoassay developed for field sampling, and smart sampling where the sample preparation steps proteolysis and immunoaffinity are integrated in the sampling. In the end we discuss the technology readiness and remaining barriers to clinical translation.