Wireless gas detection with a smartphone via rf communication

Abstract

Chemical sensing is of critical importance to human health, safety, and security, yet it is not broadly implemented because existing sensors often require trained personnel, expensive and bulky equipment, and have large power requirements. This study reports the development of a smartphone-based sensing strategy that employs chemiresponsive nanomaterials integrated into the circuitry of commercial near-field communication tags to achieve non-line-of-sight, portable, and inexpensive detection and discrimination of gas-phase chemicals (e.g., ammonia, hydrogen peroxide, cyclohexanone, and water) at part-per-thousand and part-per-million concentrations.

Keywords: NFC; RFID; nanomaterials; sensor; wireless.

Fig. 1.

Conversion of an NFC tag into a CARD enables wireless rf detection of chemical analytes with a smartphone. NFC-enabled smartphones communicate with NFC tags by simultaneously energizing the NFC tag with an alternating magnetic field (f = 13.56 MHz) through inductive coupling and transferring data by signal modulation. NFC tags are converted into CARDs by disrupting the LCR circuit (step 1) and recompleting the circuit with a stimuli-responsive variable circuit component by drawing (step 2) with solid sensing materials.

Fig. 2.

The presence of an analyte influences the power transfer between the smartphone and CARD. (A) Average (n = 5) reflection coefficient (S₁₁) of (1) baseline (no tag present), (2) unmodified NFC tag, (3) circuit-disrupted tag, (4) CARD-2, or (5) CARD-2 in the presence of cyclohexanone (equilibrium vapor pressure at ambient temperature and pressure) for 5 s and (6) for 1 min. (B) Average (n = 5) estimated power transfer (P_t) (13.53–13.58 MHz) from SGS4 to CARDs described in 1–6.

Fig. 3.

CARDs can be programmed to detect different concentrations of analyte. (A) Response of CARD-1A to four 5-min exposures of NH₃ (35 ppm) at 20-min intervals as monitored with a SGS4 (Top) and a multimeter (Bottom). Shaded boundary indicates estimated R_t based on the trace shown. (B) Response of CARD-1A (blue) and CARD-1B (orange) to a single 5-min exposure of NH₃ at two different concentrations (4 ppm and 35 ppm) as monitored with a SGS4 (Top) and a multimeter (Bottom). Shaded boundary indicates estimated R_t based on the traces shown.

Fig. 4.

Arrays of CARDs enable identification and discrimination of analytes. Response of programmed (n = 3) (A) CARD-1A, (B) CARD-1C, (C) CARD-2, and (D) CARD-3 to single 5-min exposures of (1) NH₃ (35 ppm), (2) H₂O₂ (225 ppm), (3) cyclohexanone (335 ppm), and (4) H₂O (30,000 ppm) as monitored with a SGS4 (Top) and multimeter (Bottom). Shaded boundary indicates estimated R_t for each respective CARD based on the traces shown. Compiled binary SGS4 responses (E) of CARD-1A, -1C, -2, and -3 codify the identity of the gases tested in this study.