A challenge associated with moving to human subjects is that the device requirements are much more stringent than for animals. For example, for human use an ideal device should be minimally invasive and allow for safe and easy insertion, wear, and removal. In support of this, and to increase design freedom, here we have employed ex-vivo sensors coupled to the dermis via FDA-approved, hollow microneedles (Figure ) that, because they penetrate less than 700 µm, are generally painless and avoid bleeding. This design also only introduces one foreign material, silicon, directly to the body, lowering the risk for immune response or unwanted materials leeching into the body. Finally, the ex-vivo placement of the sensors in this design also allows for additional "modules," such as a protective membrane or components supporting preconcentration of the analyte , to control the sensing environment in ways that cannot be achieved with indwelling sensor.