Narrowband quadrupole resonance (QR) probes were developed from thin-film high-temperature superconducting (HTS) resonators. The QR probes are useful in analyte-detection systems, in particular for the detection of nitrogen-containing compounds. Embodiments of the invention provide greater than an order of magnitude improvement in sensitivity and the ability to reject RF interference sources located outside the pass-band of a superconducting QR probe. Methods and apparatus are described for analyte detection and resonance frequency adjustment.