Artificial Cell Membrane Systems for Biosensing Applications

[Zoepin]

For the second half of the week, I am looking more into biosensors. This paper is very oriented towards chemistry and electronics but I believe is of value. It gives insight on a different type of biosensors, artificial cell membranes.

Artificial Cell Membrane Systems for Biosensing Applications

https://pubs.acs.org/doi/full/10.1021/acs.analchem.6b04744

Why use biological membranes as biosensors?

Because the biological membrane engages in almost every communication between cell/organelle and it's surroundings, membrane-associated proteins and lipid molecules have become a significant focus of efforts to identify new pharmaceutical drug targets. Furthermore, the functionality of the biological membrane makes it ideal for biosensing applications, as it inherently fulfils the necessary conditions of a sensor.

What is an artificial biosensor membrane?

• Lipid vesicles, which encapsulate an aqueous phase
• Planar membrane system, which can be further classified into supported bilayers, suspended bilayers, and nanodiscs.

This review focuses on membrane biosensor platforms that use suspended lipid bilayers coupled with electrical detection technologies. The suspended bilayer, also known as a free-standing bilayer, electrically divides two aqueous chambers. By insertion of transmembrane proteins as the sensing elements, the suspended bilayers form versatile chemical sensing systems that are compatible with electronics

Fundamentals of lipid bilayer systems (biological and artificial)

Phospholipids (amphiphilic molecules) that organize themselves in the form of a bilayer in aqueous solution. Typical phospholipids have a molecular weight of approximately 1 kDa, and form a bilayer of 5-nm thickness. Able to suppress the permeation of water-soluble molecules High membrane resistance of over 1 MΩ·cm2 Permeability to sodium ions

Formation of bilayers

Using microfluidics

• The Behrends group automated a method and the products are commercialized by Nanion Technologies
• Droplet contact method

Protein insertion into a lipid bilayer platform

Pore-forming toxins (gramicidin, alamethicin, and α-hemolysin) are soluble as monomers. => spontaneously bind to the lipid bilayer membrane and form transmembrane pores Insoluble proteins =>reconstituted into lipid vesicles before insertion into the bilayer membrane

Membrane pore biosensors

Nanopore coupled to an enzyme sensors for DNA sequencing The enzyme, such as a polymerase or helicase, binds to the DNA and “ratchets” the DNA through the nanopore. This significantly slows the translocation velocity down to a few tens of milliseconds per base, which is an adequate dwell time to allow single-nucleobase discrimination.

Nucleotide sequence within a nanopore for diagnosis and analysis The presence of a target sequence is discriminated using complementary sequences within the nanopore. One application of this is in the diagnosis of tumor-derived circulating microRNAs.

Pore-based chemical sensor to detect ions, organic molecules, peptides and even larger molecules such as viruses.

The article goes more in depth in how the different systems work, their limitations and possible improvements.

Future directions

• The applications could be used to detect biomarkers from body fluids and for VOC (volatile organic compound) analysis, including exhaled gas diagnostics, odorant sensors, explosives, noxious gas, and illegal drug detectors.
• For diagnostic use,lLigand-gated ion channels will become one of the model sensor elements, since they can recognize single molecules with a given specificity and sensitivity, and transduce molecular binding events to an ionic current that is compatible with electronic devices.

[research555]

If i got this right then it is just a lipid nanoparticle with a transmembrane protein right?

[Zoepin]

Yes that is right. The basic structure is a lipid bilayer or vesicle. Those can be produced using microfluidics or bought from producing companies. The lipid structure is then 'customed' by adding one or various proteins to reach a specific goal. This paper is mostly about pores and nanopores but other proteins can be added to form complex cell membranes. That way, a biological membrane can be more or less mimicked or the complexe can be used for a completely different application. For example, the paper develops an idea on sequencing.