Tailored surfaces for biorecognition, bioanalysis and sensing applications

Our research includes the development of new sensors and analytical techniques based on novel immobilized lipid structures such as supported lipid membranes, immobilized liposome layers and immobilized lipodisks. These lipid structures consist of a bilayer of lipids similar to what is found in the living cell membrane. Antibodies, receptors, and other relevant molecules can be embedded or attached to the lipid membrane, providing it with sensing capabilities. Furthermore, the lipid membrane itself can interact with molecules in solution producing a measurable response when the appropriate technique is employed.

The following are the main projects being carried out within this topic:

Association of antimicrobial peptides with immobilized lipodisks

The affinity of antimicrobial peptides to lipodisks is characterized by immobilizing the lipodisks onto QCM-D sensors. The binding of the peptides to the lipodisks is recorded as shifts in the oscillation frequency, which, in turn, are related to the amount of peptide that is bound to the disk. Association isotherms can thus be obtained. This allows for optimization and careful design of peptide loaded lipodisks for therapeutic applications.

Lipodisk and proteolipodisk chromatography

Lipodisks can be covalently coupled to porous silica particles suitable for HPLC. The resulting chromatography columns can be used to study the membrane partition of relevant molecules, such as existent therapeutic drugs. Furthermore, the lipodisks can be decorated with peripheral and integral membrane proteins, generating proteolipodisks allowing the detailed study of protein-solute interactions. This can be developed into accurate methods for fragment screening leading to the discovery of potential candidates for new therapeutic drugs.

Bioelectrochemical tools for the study of ion partition and for the detection, recognition and quantification of ions in solution

Given that most therapeutic compounds are charged, it is of extreme interest to develop a system that can directly determine the standard partition coefficient for the partitioning of ions between water and lipid bilayers. This is a universal parameter describing the relative affinity of ions for lipid membranes. In our lab we apply the reduction of coenzyme Q10 embedded in gold-supported lipid membranes to trigger the transfer of cations from the solution into the membrane. From this process the free energy of ion transfer and, therefore, its standard partition coefficient can potentially be extracted.

We are also working on the development of electroactive lipid membranes in which an oxidation reaction can be coupled with the transfer of anions into the membrane.  This will allow expanding the range of analytes that can be studied with the developed method.

The ions that can eventually be studied are very common and important pharmaceutical compounds, including, among others: ibuprofen, warfarin, diclofenac, indomethacin, naproxen, lidocaine, alprenolol, etc. We aim at establishing a new analytical method for the analysis of the cell membrane partition of these substances. Finally, the same experimental setup can be used to build sensors to detect, recognize and quantify these substances in body fluids such as sweat, urine and plasma.

Among other lines of research, we aim at developing a Coenzyme Q10-based sensor able to detect and quantify acetylcholine, an important neurotransmitter that can be used as a marker for the early diagnose of neurodegenerative diseases.

On-plate enrichment of phosphorylated peptides on mesoporous TiO2 and physicochemical characterization of TiO2-phosphopeptide interactions

We have developed a new method for enrichment of phosphorylated peptides from a complex mixture using custom MALDI target plates modified with mesoporous TiO2 spots and stripes. The latter allow also separating the phosphopeptides by degree of phosphorylation. With the help of these methods, we have been able to detect previously unreported phosphorylation sites in, e.g., proteins originating from human adenovirus particles.

We are also interested in elucidating the physic chemical parameters describing the binding of phosphopeptides to mesoporous titanium dioxide, thus allowing the further development of more accurate enrichment methods for both quantitative and qualitative phosphopeptide analyses.