Solid‐Phase Microextraction: A Complementary In Vivo Sampling Method to Microdialysis

Abstract

Given the intricate organization of the brain, tissue sampling for chemical profiling studies have always been a challenging task. It is often exceptionally difficult to obtain homogeneous samples for in vitro/ex vivo experiments without altering or losing valuable information. The obvious approach has been to develop in vivo analytical methods that may cause minimal perturbation to this complex chemical network so as to improve overall reliability of acquired information. Methods such as biosensors and microdialysis (MD) are among sampling methods applied to in vivo brain chemical profiling studies despite their unique challenges. MD is a well-established in vivo analytical sampling method used over the years for monitoring often low-molecular-weight hydrophilic compounds from the interstitial space. The successful application of the method to neuroscience, especially monitoring of neurotransmitters, led to its expansion to a wider range of analytes, including drugs, [1] metabolites, [2] and peptides. [3] A major challenge, however, associated with MD is its difficulty in sampling hydrophobic compounds. Hydrophobic compounds are often highly protein-bound and bind to the MD probe and tubing, thereby affecting relative recovery. The addition of modifiers, such as bovine serum albumin, glycerol in water, [4] or cyclodextrin, [5] is among the approaches that have been used to prevent hydrophobic interactions and to improve relative recoveries. But these techniques often may complicate the pharmacology of the neurological analytes, as the additives are known to interact with the tissue surrounding the probe. [6] Thus, in typical global metabolomics studies, for example, the composition of a measured metabolome can be significantly affected by the analytical procedure, leaving the analysts with results which likely do not adequately reflect accurate composition of the metabolome during sampling. [7] In effect, it will compromise the already challenging efforts in diagnosis, prognostics, and searching for potential biomarkers for therapeutic purposes. Herein, we demonstrate a novel application of solid-phase microextraction (SPME) for in vivo sampling for brain study. For the first time an application of in vivo SPME as a complementary method to MD for braintissue bioanalysis has been presented. Our technique was first validated against MD in targeted analysis of selected neurotransmitters. Their complementary nature was subsequently shown in global profiling of the brain metabolome. From the profiling study, SPME detected groups of lipids such as gangliosides, fatty acids, and lysophospholipids, which are of particular interest in relation to neurodegenerative diseases. SPME derives its selectivity from the extracting sorbent type. Thus, SPME provides the needed flexibility to analysts to tailor investigations to specific biologically hydrophilic/ hydrophobic compounds. For a global study of the metabolome, however, the sorbent choice is one of low selectivity; that is, the sorbent chemical property must enhance simu...

Fast Quantitation of Target Analytes in Small Volumes of Complex Samples by Matrix‐Compatible Solid‐Phase Microextraction Devices

“…single cells [13] ), but can also diminish potential damage caused during in vivo sampling. [9] Although the use of small metal probes for the analysis of single cells and tissue has already been reported, [6,13] owing to the low sorption capacity and non-specific affinity of the metal surface (poor inter-device reproducibility), their application is limited to the determination of compounds present at high concentrations (e.g. phospholipids).…”

“…[10] Given the multiple advantages of this technique, including its feasibility to be coupled to different analytical instruments,S PME has been widely used for analysis of complex matrices such as biofluids,t issues,a nd food samples. [1,[9][10][11][12] Herein our main objective is to introduce two new SPMEbased strategies that allow for the analysis of samples characterized by as mall volume and/or size.O wing to the thin nature of the coatings (Ø 10 mm), fast extraction/ enrichment of target analytes can be achieved with the use of these devices,e ven when sampling from complex matrices. Theproposed devices can be composed of either amini-fiber (Figure 1), or ac oated blade (Figure 2), allowing for extraction of analytes to be performed either by immersing the mini-fiber into the matrix, or by spotting the sample onto the coated blade.The miniaturized fiber is consisted of apolypyrrole (PPy) coated stainless steel micro-tip that can be conveniently interfaced with MS instrumentation via chromatography,o rd irectly interfaced via nano-electrosprayionization (nano-ESI).…”

“…Then, PPy was electrochemically coated onto the surface, using trifluoroacetic acid (TFA), and cetyltrimethylammonium bromide (CTAB) [16] as counter-ions (a detailed description of the experimental procedure is provided in the Supporting Information). Coatings of two different lengths, either of 150 mm( conical-shape) or 500 mm( cylindrical and conical shape), and with ac oating thickness 5 mm( see Figure S5 in the Supporting Information), were applied onto the needles.S hort coatings were intended to sample micro objects of interest such as drops,s mall organisms,o rs ingle cells,w hile cylindrical tips were envisioned to sample larger volumes with the aim to minimize invasiveness (e.g.i nvivo sampling of brain tissue [9] ). Ac omparison between the extraction capabilities of aP Py-CTAB coated tip and ab are wire showed that the extraction efficiencyofthe PPy-CTAB is at least 100-times higher than the one of the bare wire ( Figures S9 and S10).…”

Headspace versus Direct Immersion Solid Phase Microextraction in Complex Matrixes: Investigation of Analyte Behavior in Multicomponent Mixtures

“…This can be attributed to the miniaturized design of the extraction phase, which literally maintains the "physiological integrity" of the system investigated. 30,38 The aforementioned characteristics, among others, are responsible for the successful implementation of SPME in metabolomics studies applied to plant-based systems, but also to other living organisms 10,39,40 . After assessing the solid porous coatings and their behavior towards saturation and competitive adsorption in aqueous medium (with no solids matrix components), further experiments were carried out using a starch gel system as a model-matrix that closely mimics the texture consistency of fruits and vegetables.…”

Study of Viability of Solid-Phase Microextraction, in vivo, in the Extraction of Microbial Volatile Organic Compounds Associated to the Pigment Production Process by the Monascus Fungus, in Submerged Fermentation

“…7 Recently, the SPME has been used to study samples containing living materials, providing satisfactory results as to the selectivity and flexibility to adapt to several analytes of biochemical interest, including some associated with metabolome. 8 Compounds which are product of biosynthesis, such as alcohols, ketones, esters, and compounds containing sulfur were also successfully studied in living organisms through this technique. 5 In this study it is evaluated the viability of use of a method involving solid-phase microextraction, in vivo SPME, in the extraction of MVOCs, associated with the pigment production process by the Monascus fungus.…”