Paper-based immunocapture for targeted protein analysis

Advancements in clinical approaches, analytical methods, and smart sampling for LC-MS-based protein determination from dried matrix spots

Determination of proteins from dried matrix spots using MS is an expanding research area. Mainly, the collected dried matrix sample is whole blood from a finger or heal prick, resulting in dried blood spots. However as other matrices such as plasma, serum, urine, and tear fluid also can be collected in this way, the term dried matrix spot is used as an overarching term. In this review, the focus is on advancements in the field made from 2017 up to 2023. In the first part reviews concerning the subject are discussed. After this, advancements made for clinical purposes are highlighted. Both targeted protein analyses, with and without the use of affinity extractions, as well as untargeted, global proteomic approaches are discussed. In the last part, both methodological advancements are being reviewed as well as the possibility to integrate sample preparation steps during the sample handling. The focus, of this so-called smart sampling, is on the incorporation of cell separation, proteolysis, and antibody-based affinity capture.

One-step functionalization of paper and simplified antibody immobilization for on-the-spot immunocapture from dried serum in liquid chromatography-tandem mass spectrometry based targeted protein determination

This work aimed to simplify and improve the process of binding monoclonal antibodies (mAbs) covalently to filter paper for use in dried blood spot sampling, enabling instant capture of protein biomarkers for targeted protein determination. Incorporating the necessary immunocapture sample preparation step in the initial sampling stage saves time and reduces the workload. The biomarker human chorionic gonadotropin (hCG) was used as the model analyte. The antibody-based paper samplers were prepared by functionalizing paper discs (6 mm) through a simple reaction using divinyl sulfone (DVS). After DVS activation, the paper discs were incubated with E27 hCG mAbs, followed by 0.05% tween/phosphate buffer saline to block the surface. After sample application and drying, the discs only needed to be washed before tryptic digestion and finally analysed on a nanoliquid chromatography-tandem mass spectrometry system. The finished DVS-mAbs samplers could selectively capture hCG (100 ng/mL) from human serum, with a recovery of 50%. Sample clean-up reduced the number of identified proteins from 132 to 82 before and after wash, respectively, with a 70% reduction in serum albumin signal while still retaining hCG on the sampler during the washing protocol. An evaluation of the samplers revealed excellent linearity (R2  = 0.9995) for hCG in serum with relative standard deviations below 15%. This work has presented the first ever reported paper samplers immobilized with antibodies utilizing DVS chemistry, showing promise in the future of paper-based sampling.

Smart sampling as the "Spot-on" Method for LC-MS protein analysis from dried blood spots

This perspective explores the feasibility of smart sampling with dried blood spots for the determination of proteins and peptides from human biomatrices using liquid chromatography coupled to mass spectrometry for clinical purposes. The focus is on innovative approaches to transform filter paper from a mere sample carrier to an active element in sample preparation, with the aim of reducing the need for extensive and intensive sample preparation in the conventional sense. Specifically, we discuss the use of modified cellulose to integrate sample preparation at an early stage of sample handling. The use of paper immobilized with either trypsin or monoclonal antibodies for protein digestion and affinity clean-up is discussed as a potential benefit of starting sample preparation instantly at the moment of sampling to optimize time efficiency and enable faster analysis, diagnosis, and follow-up of patients.

Dried blood spots in clinical lipidomics: optimization and recent findings

Dried blood spots (DBS) are being considered as an alternative sampling method of blood collection that can be used in combination with lipidomic and other omic analysis. DBS are successfully used in the clinical context to collect samples for newborn screening for the measurement of specific fatty acid derivatives, such as acylcarnitines, and lipids from whole blood for diagnostic purposes. However, DBS are scarcely used for lipidomic analysis and investigations. Lipidomic studies using DBS are starting to emerge as a powerful method for sampling and storage in clinical lipidomic analysis, but the major research work is being done in the pre- and analytical steps and procedures, and few in clinical applications. This review presents a description of the impact factors and variables that can affect DBS lipidomic analysis, such as the type of DBS card, haematocrit, homogeneity of the blood drop, matrix/chromatographic effects, and the chemical and physical properties of the analyte. Additionally, a brief overview of lipidomic studies using DBS to unveil their application in clinical scenarios is also presented, considering the studies of method development and validation and, to a less extent, for clinical diagnosis using clinical lipidomics. DBS combined with lipidomic approaches proved to be as effective as whole blood samples, achieving high levels of sensitivity and specificity during MS and MS/MS analysis, which could be a useful tool for biomarker identification. Lipidomic profiling using MS/MS platforms enables significant insights into physiological changes, which could be useful in precision medicine.

On the spot immunocapture in targeted biomarker analysis using paper-bound streptavidin as anchor for biotinylated antibodies

The modification of an easily available resource like paper to circumvent expensive or intensive sample pretreatment could be the answer to sample analysis in resource-poor regions. Therefore, a novel on-paper device combining sample collection with affinity sample pretreatment is introduced here. Universal smart affinity samplers are produced by a simple KIO₄-mediated oxidation of cellulose, which functionalizes the paper. This is followed by immobilization of streptavidin. Streptavidin serves as a universal anchor for biotinylated antibodies, enabling simple preparation of tailor-made affinity samplers. The functionality of the device was tested using a model protein (human chorionic gonadotropin, hCG) and biotinylated anti-hCG antibodies for affinity capture. In a laboratory setting, the performance was demonstrated, and a 14-fold increase of target binding compared to binding without bmAb was achieved. The recovery of hCG captured with bmAb-treated samplers was determined to be 33% and comparable to previously described affinity capture approaches. Application of the smart affinity samplers to human serum containing hCG showed an R² of 0.98 (200–1000 pg mL⁻¹), precision of ≤ 9.1% RSD, and estimated limit of detection of 65 pg mL⁻¹. Although further optimization and validation are necessary prior to application to real samples in clinical settings, the potential of the device for use in determination of low abundant biomarkers in complex samples has been demonstrated.

Next-Generation Dried Blood Spot Samplers for Protein Analysis: Describing Trypsin-Modified Smart Sampling Paper

This paper describes smart sampling paper to be used for bottom-up protein analysis. Four different manners to immobilize trypsin on cellulose were evaluated. Untreated paper, potassium-periodate-functionalized paper (with and without post-immobilization reduction) and 2-hydroxyethyl methacrylate (HEMA)/2-vinyl-4,4-dimethylazlactone (VDM)-functionalized paper were all used to immobilize trypsin. For the evaluation, Coomassie Brilliant Blue staining of proteins on paper and the BAEE trypsin activity assay needed to be modified. These methods allowed, together with data from mass spectrometric analysis of cytochrome C digestions, us to acquire fundamental insight into protein binding, and trypsin action and activity on paper. All functionalized discs bind more protein than the untreated discs. Protein binding to functionalized discs is based on both adsorption and covalent binding. Trypsin immobilized on potassium-periodate-functionalized discs exhibits the highest trypsin activity when using cytochrome C as substrate. It is proven that it is trypsin attached to paper (and not desorbed trypsin) which is responsible for the enzyme activity. The use of discs on complex biological samples shows that all functionalized discs are able to digest diluted serum; for the best-performing disc, HEMA-VDM functionalized, up to 200 high-confidence proteins are qualified, showing its potential.

A paper-based chemiluminescence immunoassay device for rapid and high-throughput detection of allergen-specific IgE

The fast and precise detection of potential allergen-specific immunoglobulin E (sIgE) is imperative for the diagnosis and appropriate treatment of allergic diseases. In this study, we have successfully fabricated a novel paper-based immunoassay device for the detection of sIgE in allergic diseases. We used Can f 1, one of the main dog allergens, as a model allergen to detect sIgE in human sera. To achieve excellent performance, the experimental parameters were optimized. Further, we extended this device for potential applications in the clinical diagnosis of allergic diseases: worthwhile clinical performance in the detection of allergens was achieved as compared to that achieved by commercial enzyme-linked immunosorbent assay (ELISA) kit. Therefore, it was proven that this strategy has the advantages of high-throughput, rapid, sensitive, and highly accurate detection of trace amounts of sIgEs. Furthermore, by simply changing the antigen and antibody, this device could be used for the high-throughput detection of other allergens, so as to achieve multiallergen detection and appropriate desensitization therapy, thereby making it promising in the determination of allergic diseases in clinics.