<p>Localized surface plasmon resonances (LSPRs) hold great promise for biomolecular sensing due to their strong field enhancement and deep subwavelength (~ 10&#xa0;nm scale) field confinement. Commonly, there is a trade-off between sensitivities and dynamic ranges for sensors. Here, we experimentally demonstrate an LSPR sensor that achieves both high sensitivities and large dynamic ranges for biomolecular detection. By employing huge contrasts of refractive indices between the analytes and air, the bare gold nanorods (bGNRs), where surface ligands are removed, are quite sensitive to bovine serum albumins (BSA) adhered to bGNRs. Experimentally, one bGNR is used to detect BSA solutions with different concentrations, and the averaging effect of multiple GNRs is eliminated. As a result, the smallest detection concentration (detection limit) reaches <i>C</i>_min ≈ 410 pM, and the largest detection concentration is as high as <i>C</i>_max ≈ 10 µM. So, the dynamic range is as large as <i>DR</i> ≈ 10×lg (<i>C</i>_max/<i>C</i>_min) ≈ 44 dB. These high-sensitivity biomolecular sensors with large dynamic ranges by using one deep-subwavelength bGNR (~ 4 × 10^− 4 <i>λ</i>³) might find important applications in trace and small-scale detection chips.</p>