Abstract: Disclosed herein is a novel phenomenon to create a nano-confined, dopant-free, electron spin-dependent fluorescence (SDF) in spider silk by fundamentally transforming its local molecular structure with femtosecond-pulses (206), having fluence below an ablation threshold. Electron-spin dependence of the fluorescent patterns created on the silk sample are confirmed by measuring the fluorescence intensity at different microwave frequencies. The fluorescent intensity exhibits microwave magnetic resonances at 2.88 GHz and 1.44 GHz at room-temperature. The SDF in laser-transformed silk can thereby enable a new-class of tough yet elastic silk-based quantum sensor and hybrid nano-mechanical ultrasensitive cantilevers on a micro-chip.