An optical whispering gallery mode resonator can spin light around the circumference of a tiny sphere millions of times, creating an ultrasensitive microchip-based sensor for multiple applications. Engineers have developed an innovative way to grow on-chip glass microspherical shells with incredible sensitivities that potentially can be used for motion, temperature, pressure or biochemical sensing.

Chip-scale glass microspherical shell sensor array blown on a silicon substrate. Insert is a near-perfect spherical shell.
(Credit: Tadigadapa Lab/ Penn State)

The hollow borosilicate glass spheres are blown from sealed and pressurized cylindrical cavities etched into a silicon substrate. Using a glassblowing technique, the thin glass wafer, under high heat and external vacuum pressure, forms an almost perfect bubble. The researchers grew arrays of spheres from 230 µm to 1.2 mm in diameter with wall thicknesses between 300 nm and 10 µm.

The team discovered that the key to making a high-quality sensor lay in making sure that the equatorial plane of the sphere, its center, is above the surface of the chip. This result will have particular significance for lab-on-a-chip biophysical sensing for disease sensing.