A PDMS dermal patch for non-intrusive transdermal glucose sensing M. Paranjape a,b,* , J. Garra b , S. Brida b , T. Schneider b,d , R. White b,d , J. Currie a,b,c a Department of Physics, Georgetown University, Washington, DC 20057, USA b Georgetown Advanced Electronics Laboratory (GAEL), Washington, DC 20057, USA c Department of Pharmacology, Georgetown University, Washington, DC 20057, USA d Science Applications International Corporation (SAIC), McLean, VA 22102, USA Received 1 July 2002; received in revised form 21 November 2002; accepted 21 November 2002 Abstract This paper describes the fabrication of an adhesive bandage comprised of multiple, compliant polydimethylsiloxane (PDMS) micro-fluidic elements to perform controlled and non-intrusive transdermal sampling of glucose, or any other bio-molecule present in interstitial fluids. The patch-like device, to be worn on the skin, has PDMS component layers that form vertically oriented micro-fluidic channels and reservoirs. In addition, micro-heater elements are integrated onto the PDMS layer that will be in contact with the skin, and are used to thermally ablate tiny micro-pores through only the dead-skin layer, allowing for easier diffusion of normally trapped bio-molecules, such as glucose, to the skin surface. The dermal patch, containing micro-channels and fluid-encapsulated reservoirs, assist in the transport of glucose molecules from just beneath the dead-skin layer to a colorimetric detection membrane situated on top of the bi-layer PDMS patch. This paper will focus on the fabrication of the prototype PDMS patch and the challenges encountered during wafer-scale batch production. Preliminary in vitro studies using human graft skin samples are included to illustrate the non-inflammatory micro-ablation procedure. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Polydimethylsiloxane (PDMS); Bio-molecule; Transdermal glucose sensing 1. Introduction A means of non-intrusive, real-time sampling of specific bio-molecules from the interstitial fluid would provide an important and convenient means towards monitoring indi- viduals prone to high health risks, such as those exposed to environmental, chemical, or biological hazards, have pre- disposed health conditions, or need to be closely monitored following illness. The polydimethylsiloxane (PDMS) based skin patch presented here is a novel bioMEMS device relying on the advances made in microfabrication technol- ogies related to both PDMS and thick SU-8 photoresist mold processing [1–7]. The prototype of the PDMS patch will be used to sample glucose, however the development of this microsystem will provide an enabling technology for trans- dermal sampling of other bio-molecules that do not normally diffuse across the skin. Typically, bio-molecules of medical relevance are unable to reach the skin surface due to a combination of relative size and their inability to diffuse across the densely packed hydrophobic layers of dead-skin cells (stratum corneum (SC)). The overall thickness of the dead-skin layer averages around 50 mm, and in an unbroken state, acts as a very effective seal against interstitial fluid leakage and maintains bio-molecular containment. When this seal is compromised, the interstitial fluid and the bio- molecules contained therein become available on the skin surface. The method by which large bio-molecules, such as glu- cose, can reach the skin surface for subsequent analysis by the PDMS patch is accomplished by opening a microscopic region of the stratum corneum to allow the glucose (and other bio-molecules) to diffuse naturally to the skin surface. By locally applying a high temperature in proximity to the skin surface, the dead-skin cells can be thermally ablated, or vaporized, using micro-heaters integrated on the PDMS layer closest to the skin surface. By regulating the current through a resistive heater and its time duration, the generated heat pulse can be controlled to such an extent that neither the living tissue nor the nerve endings are affected by the micro- heater elements (refer to Fig. 1). Glucose monitoring with the PDMS patch has many far- reaching applications, ranging from civilian to defense interests. In the former, a non-intrusive means of on-demand monitoring of blood-sugar levels in diabetics would alleviate the grossly invasive, distracting, and uncomfortable finger Sensors and Actuators A 104 (2003) 195–204 * Corresponding author. Tel.: þ1-202-687-6231; fax: þ1-202-987-2087. E-mail address: paran@physics.georgetown.edu (M. Paranjape). 0924-4247/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0924-4247(03)00049-9