Biosafety Cu/CaCu3Ti4O12 metacomposites for broadband weakly epsilon-negative response

Weakly epsilon-negative (ε' < 0, EN) response media are the key to new single-molecule detection technologies and show promising application prospects in disease diagnosis, microwave-powered cancer treatment, in vivo detection, imaging, cell tracking and monitoring of disease occurrence mechanisms. The regulation of weakly EN responses is related to the detection accuracy of biomedicine. Therefore, based on the percolation theory, we created a set of Cu/CaCu₃Ti₄O₁₂ (Cu/CCTO) metacomposites. The irregular dendrite Cu particles were used as the building blocks for constructing 3-dimensional conductive networks in CCTO matrix. Electrical percolation occurs when the Cu content is between 30 wt% and 40 wt%, which marks two dielectric response mechanisms: electric dipole resonance and plasmonic oscillation. The epsilon-negative response (ε' < 0, EN) band of the former excitation is relatively narrow, but with the increase of Cu content, the resonance intensity increases, and the accompanying epsilon-near-zero (-1 < ε' < 1) moves to low frequency. Above the percolation threshold, once the effective electron concentration required for plasmonic oscillation is achieved, we successfully obtain a EN response for the entire test band and achieve a weakly negative permittivity (-100 < ε' < 0) across 450 MHz-1 GHz region. The inductance characteristic and EM shielding effect of EN response are elucidated by equivalent circuit model and EM simulation technique. Finally, we evaluated the biocompatibility of Cu/CCTO metacomposites for cell growth and human tissue, which provided a research basis for the practical application of binary percolative metacomposites.