Gregory Damhorst, PhD

The following research descriptions reflect my NIH biosketch

Microscale biosensors for HIV detection and viral load determination

The Human Immunodeficiency Virus (HIV) pandemic has resulted in more than 34 million deaths worldwide and another 37 million people are living with HIV today. Among the barriers to bringing the standard of care to those facing HIV infection is the limited availability of technologies to meet the needs of diagnosis and clinical monitoring, particularly viral load quantification. Recent understanding has underscored the importance of viral load as a core marker in clinical management, not only for maintaining the health of the HIV-positive individual, but also in preventing transmission of the virus to others.

In this work, we developed approaches to detection and quantification of HIV from whole blood samples. First, we developed a technique called ion-release impedance spectroscopy which employs a simple ion-filled liposome as the signal component of a microfluidic immuno-capture and impedance-based biosensor. More recently, we have implemented an alternative approach which employs loop-mediated isothermal amplification (RT-LAMP) for detection of viral RNA in a whole blood sample. A major aspect of the novelty of the RT-LAMP approach was to show the potential for direct detection in lysed whole blood with limited sample processing. The reaction was demonstrated in nanoliter droplets and imaged with a consumer smartphone.

This work was the focus of my doctoral thesis which I led and developed with support of colleagues in the laboratory of Dr. Rashid Bashir in the Department of Bioengineering at the University of Illinois at Urbana-Champaign.

Related publications:
  1. Damhorst GL, Smith CE, Salm EM, Sobieraj MM, Ni H, Kong HJ, Bashir R, "A liposome-based ion release impedance sensor for biological detection". Biomed Microdevices. 2013 Oct;15(5):895-905. doi: 10.1007/s10544-013-9778-4. PubMed PMID: 23793417; PubMed Central PMCID: PMC4079459.
  2. Damhorst GL, Duarte-Guevara C, Chen W, Ghonge T, Cunningham BT, Bashir R, "Smartphone-Imaged HIV-1 Reverse-Transcription Loop-Mediated Isothermal Amplification (RT-LAMP) on a Chip from Whole Blood," Engineering (Beijing). 2015 Sep;1(3):324-335. Epub 2015 Oct 16. PubMed PMID: 26705482; PubMed Central PMCID: PMC4687746.
  3. Damhorst GL, Kooiman JM, Bashir R, "HIV-1 IIIB Capture from Whole Blood on Magnetic Microparticles". 38th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Orlando, FL. 16-20 August 2016.

An impedance-based microfluidic cytometer for blood cell enumeration

Blood cell counting is ubiquitous in healthcare; however, the use of blood counts in clinical diagnostics is currently limited to settings which have established infrastructure for central sample processing and reporting. Our work has addressed two specific areas in which point-of-care blood cell counting could improve the standard of care for millions of individuals worldwide: in management of HIV infection and basic applications of the complete blood count.

The core technology is a microfluidic cytometer designed to receive a 10 microliter whole blood input (as from a fingerstick). Selective cell lysis and dilution of the sample is performed on-chip in precisely-controlled microfluidic channels followed by impedance-based cell counting which is capable of distinguishing many blood cell types based on size and membrane properties. Further discrimination of cell sub-type (e.g. CD4+ T lymphocyte enumeration) is achieved with immune-affinity capture in an antibody-functionalized microfluidic chamber which, coupled with pre-capture and post-capture cell counting allows for a differential count of specific populations of interest. Future work aims to apply this core technology to bedside detection of novel biomarkers of inflammatory response in medical and intensive care of the hospitalized patient.

This work was a part of my graduate training at the University of Illinois at Urbana-Champaign in the laboratory of Dr. Rashid Bashir, where I was part of a team led by Dr. Nicholas Watkins and Dr. Umer Hassan.

Related publications:
  1. Watkins NN, Hassan U, Damhorst GL, Ni H, Vaid A, Rodriguez W, Bashir R, "Microfluidic CD4+ and CD8+ T lymphocyte counters for point-of-care HIV diagnostics using whole blood," Sci Transl Med. 2013 Dec 4;5(214):214ra170. doi: 10.1126/scitranslmed.3006870. PubMed PMID: 24307694.
  2. Hassan U, Reddy Jr. B, Damhorst GL, Sonoiki O, Ghonge T, Yang C, Bashir R, "A Microfluidic Biochip for Complete Blood Cell Counts at the Point-of-Care," Technology (Singap World Sci). 2015 Dec;3(4):201-213. Epub 2015 Dec 11. PubMed PMID: 26909365; PubMed Central PMCID: PMC4761450.
  3. Hassan U, Watkins NN, Reddy B Jr, Damhorst GL, Bashir R. "Microfluidic differential immunocapture biochip for specific leukocyte counting," Nature Protocols. 2016. 11 (4) 714-726. PMID: 26963632. DOI: 10.1038/nprot.2016.038.

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