Figure 2.

Properties of nanoprobe PtP-C343. a) Absorption and emission (λ_ex = 460 nm, arbitrary intensity units) spectra of the probe and reference chromophores: PtP and C343. b) 2PA-induced emission spectra (excitation: λ_ex = 840 nm, 110 fs, 76 MHz rep. rate) at different excitation powers and power dependence (inset) for phosphorescence of a reference Pt porphyrin (PtP) without the antenna (black squares), PtP-C343 phosphorescence (white circles) and PtP-C343 fluorescence (white triangles). The data points [phosphorescence intensity (I), normalized by concentration, vs excitation power (P)], were fit to quadratic functions: I(P)=aP² (solid line). The phosphorescence deviates from the quadratic law at higher incident powers (see text and Figure 3). The fluorescence rises quadratically throughout the entire power range examined. c) Phosphorescence lifetime (τ) vs pO₂ calibration plots in pure buffer (black) and in cell growth medium containing 3 % of serum albumin (25 °C, pH 7.2) (white). Inset: 2PA-induced emission spectra (λ_ex = 840 nm) of the probe at air saturation (black) and in deoxygenated solution (gray), showing that only the phosphorescence signal (λ_max = 680 nm) responds to the change in oxygen pressure.