Aerosol Jet Printed and Photonic Cured Paper-Based Ammonia Sensor for Food Smart Packaging

In this work, we report the manufacturing and experimental analysis of low-cost and eco-friendly paper-based gas sensors for food smart packaging. The hygroscopic properties of paper help detect the presence of water-soluble gases in an environment provided with relative humidity (RH) above a given threshold (RH
$\,{>}\,75$
%) and discovering the presence of gaseous markers of the food spoilage process, such as ammonia. Carbon interdigitated electrodes were printed by aerosol jet printing (AJP) and sintered by flash lamp annealing on chromatographic paper, obtaining a mean resistance value of (
$231\,{\pm }\,20$
)
$\text{k}\Omega $
and (
$249\,{\pm }\,28$
)
$\text{k}\Omega $
for the left and right electrodes, respectively. After being tested at different RH values (75, 80, 90, and 100%), and once stabilized, they were tested with different ammonia concentrations (3, 6, 9, and 12 ppm). A proportional resistance decrease was evidenced in increasing ammonia concentration. Considering the baseline at a constant value of RH
$\,{=}\,75$
%, the sensors showed a resistance variation of 12% in the presence of the lowest concentration of 3 ppm. Three different temperatures were considered during the tests,
$5~^{\circ }\text{C}$
, 15 °C, and 25 °C, evidencing no primary influence of this parameter. Ethanol and acetone were investigated as representatives of interfering compounds such as alcohols and ketones that may be developed during food spoilage. Good selectivity was observed both by studying these compounds individually and together with ammonia. Experimental results showed that 48 ppm of acetone induced a resistance change lower than 3 ppm of ammonia, while 240 ppm of ethanol induced a resistance change comparable to 12 ppm of ammonia.