  Strategies for in-liquid micro-organism detection are crucial for the
clinical and pharmaceutical industries. While Raman spectroscopy is a promising
label-free technique for micro-organism detection, it remains challenging due
to the weak bacterial Raman signals. In this work, we exploit the unique
electromagnetic properties of metamaterials to identify bacterial components in
liquid using an array of Fano-resonant metamolecules. This Fano-enhanced Raman
scattering (FERS) platform is designed to exhibit a Fano resonance close to the
protein amide group fingerprint around 6030 nm. Raman signatures of Escherichia
coli were recorded at several locations on the metamaterial under off-resonance
laser excitation at 530 nm, where the photodamage effect is minimized. As the
sizes of the Escherichia coli are comparable to the micro-gaps, i.e 0.41
{\mu}m, of the metamaterials, its local immobilisation leads to an increase in
the Raman sensitivity. We also observed that the time-dependent FERS signal
related to bacterial amide peaks increased during the bacteria's
mid-exponential phase while it decreased during the stationary phase. This work
provides a new set of opportunities for developing ultrasensitive FERS
platforms suitable for large-scale applications and could be particularly
useful for diagnostics and environmental studies at off-resonance excitation.
