Flexible, semitransparent and robust heating arrays have been designed by grayscale printing as ready-to-use devices for point-of-care application. A perforated Ag mesh is first fabricated with tunable features by controllably varying the toner grayscale value during laser printer on PET. The resistance could be varied between 1 to 2Ω by tuning the Ag fill factor from 50 to 70%. The Ag/PET heater based on joule heating is able to attain highly stable temperatures upto ∼135°C maintained over long hours. Since temperature is directly related to resistance, this provides a fine temperature knob without any cumbersome processing steps. The merit of design allows individual heating elements to attain stable temperatures at low voltages (∼1.5V) without any interference from neighboring heaters of the array, thus resulting in a thermal library. A laptop USB with 5.1V output is able to power the thermal library for temperatures in the range of 30-60°C, useful in many practical applications. It is a multipurpose disposable chip for in-situ transmission microscopy that can be utilized for bioassay and point-of-care diagnostics, as demonstrated in the study. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.