Room-temperature optoelectronic devices that operate at shortwave and midwave infrared wavelengths (1-8 μm) can be used for numerous applications 1-5 . To achieve the operating wavelength range needed for a given application, a combination of materials with different bandgaps (e.g. superlattice/heterostructure) 6,7 or the variation of semiconductor alloy composition during growth 8,9 is used; however, these approaches involve fabrication complexity and the operating range is fixed post-fabrication. Although wide-range, active, and reversible tunability of the operating wavelengths in optoelectronic devices after fabrication is a highly desirable feature, no such platform has been yet developed. Here, we demonstrate high-performance room-temperature infrared optoelectronics with actively variable spectra by presenting black phosphorus (bP) as an ideal candidate. Enabled by the * � � 𝐸𝐸 𝑔𝑔 𝑘𝑘 𝐵𝐵 𝑇𝑇 �� (2)where 𝑚𝑚 𝑒𝑒 * and 𝑚𝑚 ℎ * are the effective masses of electrons and holes, respectively, 𝑘𝑘 𝐵𝐵 is Boltzmann's constant, and 𝑇𝑇 is temperature 36,37 . Since 𝑚𝑚 𝑒𝑒 * and 𝑚𝑚 ℎ * in bP have similar values, the effective mass ratio (𝑚𝑚 𝑒𝑒 * /𝑚𝑚 ℎ * ) is much higher than that of other small bandgap semiconductors.According to equation (2), this results in suppressed Auger recombination (longer Auger lifetime), which leads to bP's theoretical QY limit being much higher than that of other small bandgap semiconductors in the high injection regime.

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and mass-sensitive sensors, [9] but few of these have been demonstrated to be cost, power, and size effective. For instance, the widely commercialized resistance-based metal oxide sensors must typically be operated at high temperatures to enable the adsorption interactions required for transduction. [8,[10][11][12] This results in higher power consumption as operation temperatures must be adjusted by a built-in heater. While other efforts have focused on the optimization of sensing materials [4,13,14] and sensor structure, [15] the resulting devices remain far from being practically applicable due to their limited detection sensitivity and poor reproducibility under mass fabrication. [16] Therefore, effective gas sensing systems with minimal baseline drift, good selectivity, low hysteresis, and the ability to simultaneously measure multiple gases still need to be developed. In this context, silicon transistor-based sensors have shown significant promise, with key advantages in overcoming size limitations, low power sensing, and high sensitivity, [17][18][19][20][21] making them useful for trace-level gas sensing applications required in food freshness monitoring.Ammonia (NH 3 ) and hydrogen sulfide (H 2 S) are two types of marker gases for spoiling food. For high-protein foods such as eggs, dairy, and meat, off-gassed NH 3 and H 2 S serve as quality indicators of freshness. [22][23][24][25] These gases can also be emitted from rotting vegetables such as corn and spinach. [26] For simplicity, eggs and pork samples are selected for monitoring food spoilage in this work. Based on reported data, 10 mL of egg whites produces ≈100 µg of H 2 S over multiple hours. [23] After accounting for food storage volume and temperature, this means that the sensor system must be able to identify H 2 S and NH 3 gases with lower than 100 ppb detection limits and negligible cross-sensitivity. While electrochemical, colorimetric, and other sensing schemes in previous work have shown promise for gas and adulteration detection, it still remains to detect gas signatures continually and at low concentration levels for monitoring spoiling food. [24][25][26][27][28][29] Multiplexed sensing is also important-for example, humidity is another important parameter that affects food storage and spoilage, [22,[30][31][32][33][34] and thus should be simultaneously monitored with H 2 S and NH 3 . All of these requirements necessitate the deployment of sensors with high selectivity and low detection limits.Multiplexed gas detection at room temperature is critical for practical applications, such as for tracking the complex chemical environments associated with food decomposition and spoilage. An integrated array of multiple silicon-based, chemical-sensitive field effect transistors (CSFETs) is presented to realize selective, sensitive, and simultaneous measurement of gases typically associated with food spoilage. CSFETs decorated with sensing materials based on ruthenium, silver, and silicon oxide are used to obtain stable room-temperature responses t...