A method of electronically probing an oxidation-reduction reaction in an analyte-containing fluid, comprising: applying , by a first circuit, a periodic voltage excitation signal to a first electrode of a CGM sensor disposed within the analyte-containing fluid, wherein the periodic voltage excitation signal has a fundamental frequency; generating , by a second circuit while the first circuit is applying the periodic voltage excitation signal, a current measurement signal, having a magnitude of a current conveyed from the CGM sensor, wherein the current is generated by an oxidation-reduction reaction in the analyte-containing fluid, and wherein the magnitude of the current measurement signal is dependent, at least in part, on a glucose concentration in the analyte-containing fluid; sampling , by a third circuit coupled to the second circuit, the current measurement signal; providing , by the third circuit, digitized time-domain sample data representative of the current measurement signal; extracting a plurality of harmonic signals based, at least in part, on the digitized time-domain sample data, wherein the harmonic signals are harmonics of the fundamental frequency, and each harmonic signal has a corresponding strength, wherein the extracting comprises transforming the digitized time-domain sample data to digitized frequency-domain data; calculating a set of harmonic ratios based on at least a portion of the plurality of harmonic signals; accessing a harmonic relationship database, wherein the harmonic relationship database includes a plurality of vectors, wherein each vector includes a set of harmonic ratios, and wherein each vector is associated with a corresponding glucose concentration; and determining the glucose concentration in the analyte-containing fluid as the glucose concentration value associated with a vector in the harmonics relationship database matching the calculated set of harmonic ratios. applying , by a first circuit, a periodic voltage excitation signal to a first electrode of a CGM sensor disposed within the analyte-containing fluid, wherein the periodic voltage excitation signal has a fundamental frequency; generating , by a second circuit while the first circuit is applying the periodic voltage excitation signal, a current measurement signal, having a magnitude of a current conveyed from the CGM sensor, wherein the current is generated by an oxidation-reduction reaction in the analyte-containing fluid, and wherein the magnitude of the current measurement signal is dependent, at least in part, on a glucose concentration in the analyte-containing fluid; sampling , by a third circuit coupled to the second circuit, the current measurement signal; providing , by the third circuit, digitized time-domain sample data representative of the current measurement signal; extracting a plurality of harmonic signals based, at least in part, on the digitized time-domain sample data, wherein the harmonic signals are harmonics of the fundamental frequency, and each harmonic signal has a corresponding strength, wherein the extracting comprises transforming the digitized time-domain sample data to digitized frequency-domain data; calculating a set of harmonic ratios based on at least a portion of the plurality of harmonic signals; accessing a harmonic relationship database, wherein the harmonic relationship database includes a plurality of vectors, wherein each vector includes a set of harmonic ratios, and wherein each vector is associated with a corresponding glucose concentration; and determining the glucose concentration in the analyte-containing fluid as the glucose concentration value associated with a vector in the harmonics relationship database matching the calculated set of harmonic ratios. <EOS>