A simple laser-writing procedure can be used to directly create circuit components from inexpensive materials, allowing users to bypass costly lithography and deposition methods typically used for manufacturing electronics. By controlling the power and other properties of a narrow beam of laser light as it scanned the surface of a thin film of molybdenum disulfide (MoS2), Nicholas R. Glavin of the Air Force Research Laboratory, Christopher Muratore of the University of Dayton, and coworkers selectively modified the composition, crystallinity, and electronic properties of the film. The team used the procedure to pattern the amorphous MoS2 starting material, transforming microscopic regions of the film into the three basic types of materials needed to build circuitry—a conducting phase (MoO2), an insulator (MoO3), and a semiconducting phase (2H-MoS2) (shown). In a proof-of-concept study, the team used the laser-writing method to make resistors, capacitors, and other circuit components and fabricated an ammonia sensor with a detection limit below the part-per-million level (Mater. Today 2020, DOI: 10.1016/j.mattod.2020.09.036). In a follow-up study, which has not yet been peer reviewed, the researchers used the same technique to build inexpensive rapid-response sensors for SARS-CoV-2 spike proteins and influenza A hemagglutinin in saliva samples (medRxiv 2020 DOI: 10.1101/2020.11.17.20233569).