Electrochemical Biosensor for Faster Diagnosis of Alpha-1-Antitrypsin Deficiency

In the medical field, new and quicker methods for the diagnosis of diseases are sought.  Being able to diagnose the disease earlier and easier typically increases the life expectancy of a patient. As such, electrochemical biosensors provide a potentially quicker method to diagnose certain diseases.  A biosensor is a device that can directly convert biological activity into an electronic signal, which is done at the nanoscale.^[1] For a specific case, Alpha-1-antitrypsin (A1AT) Deficiency (A1AD) is an underdiagnosed disease that is caused by subtle changes in the protein composition that could possibly be detected through the use of an electrochemical biosensor.

A1AD is a potentially debilitating genetic condition that can lead to low levels of A1AT in the lungs, causing an imbalance between A1AT and human neutrophil elastase (HNE), its preferential target. This can predispose those affected to emphysema, often in the 3^rd or 4^th decade of life. Certain genetic mutations can also lead to an accumulation of A1AT in the liver, potentially leading to cirrhosis as well as early-onset emphysema. Approximately 100,000 people in the United States are estimated to be affected by A1AD, but it has been estimated that only about 10,000 have been diagnosed.  Across the globe, it is estimated that 116 million people worldwide are carriers of the S or Z forms, and another 1.1 million are estimated to have A1AD. Currently, no cure exists, and current approaches for diagnosis are insufficient as illustrated by the fact that A1AD is underdiagnosed and diagnosis is often delayed.^[2] 

More than 120 mutations have been recognized with the two most prevalent being referred to as S and Z in contrast to the M form.  These letter designations stem from where the protein migrates during isoelectric focusing, with the M form stopping in the middle and the Z form migrating the slowest of any of the mutations.^[2] Further, it has been shown that A1AT can be oxidized at the active site which reduces its ability to associate with HNE up to 2000 fold.^[3] With these issues, a new method of diagnosis is being developed. 

Quartz crystal microbalance approaches are utilized in development of fuel cell technologies, aerosol particle sizing instruments, and in other systems exploiting aspects of electrochemistry and mass changes on highly sensitive crystals. A1AT has both electrostatic and electrochemical properties.^[4] The intention of this project is to utilize the A1AT redox signature combined with substrate adsorption to develop a dual detection method. Substrate adsorption will be measured in tandem with an Electrochemical Quartz Crystal Microbalance (EQCM) system where HNE is attached to the Au electrode, and a buffered solution of A1AT is flowed over the top of the electrode.  The frequency of vibration of the crystal, which can be inversely correlated to the change in mass over time, is measured over time.  This change in mass along with electrochemical measures over time can be used to correlate to the kinetics of the inhibition of A1AT.  Any differences seen between the M form of A1AT and other forms of A1AT, both on a mass and kinetic basis, might allow for the distinction of multiple forms.