*2.1. Materials and Characterizations*

Sodium 3-mercapto-1-propanesulfonate (HS(CH2)3SO3Na, 3MPS, Aldrich, 99%, St. Louis, MO, USA), tetrachloroauric(III) acid trihydrate (HAuCl4·3H2O, Aldrich, 99.0%, St. Louis, MO, USA), sodium borohydride (NaBH4) and PBS bu ffer solution at pH = 7.4 (technical grade Aldrich, St. Louis, MO, USA) were used as received. UV–Vis spectra were acquired in H2O and MeOH solutions by using quartz cells with a Varian Cary 100 Scan UV–Vis spectrophotometer. The size distribution of AuNPs in H2O solution was investigated by means of the dynamic light scattering (DLS) technique by using a Zetasizer Nanoseries Malvern instrument, at the specific temperature (25.0 ± 0.2 ◦C and 37.0 ± 0.2 ◦C). Correlation data were acquired and fitted in reference to our previous work [51,52]. Field emission scanning electron microscopy (FESEM) images were acquired with an Auriga Zeiss

instrument, resolution 1 nm, applied voltage 6–12 kV) on freshly prepared films drop-cast from a water solution on a metallic sample holder. A Mini Spin-Eppendorf centrifuge was used for the purification of AuNPs samples (13,000 rpm, 20 min, five times with deionized water). Deionized water was obtained from Zeener Power I Scholar-UV (18.2 M Ω). A Scanvac-CoolSafe55-4 Lyophilizer was used to dry samples. Attenuated total reflection (ATR) spectra were recorded with a Bruker Vertex 70 instrument in the range of 4000–400 cm<sup>−</sup>1. High-resolution x-ray photoelectron spectroscopy (HR-XPS) experiments were carried out at the CNR BACH (Beam line for Advanced DiCHroism) [53] undulator beam line at the ELETTRA Synchrotron Radiation facility of Trieste (Italy). XPS data were collected with a pass energy equal to 50 eV, with the monochromator entrance and exit slits fixed at 20 μm. Photon energies of 386 eV, 596 eV and 1022 eV were used respectively for C1s, Au4f, P2p, B1s; O1s, N1s; Cu2p spectral regions, with an energy resolution of 0.23 eV. C1s spectra used for calibration were recorded at all photon energies. Calibration of the energy scale was made by referencing all the spectra to the C1s core level signal of aliphatic C atoms, always found at 285.00 eV, and the Au4f7/2 signal of metallic gold measured on a reference gold foil (84.00 eV Binding Energy, BE) [54,55]. A curve-fitting analysis was performed using Gaussian curves as fitting functions. When several di fferent species were individuated in a spectrum, the same FWHM value was used for all individual photoemission bands. To perform HR-XPS analysis, pristine Cu(I) complexes (A = [Cu(PTA)4] + [BF4] − and B = [HB(pz)3Cu(PCN)] and functionalized Au nanoparticles (AuNPs-A and AuNPs-B) were deposited onto TiO2/Si(111) (as to avoid any signal interference) wafer substrates by following a drop-casting procedure.

### *2.2. Preparation of Conjugate Nanoparticles*

The AuNPs stabilized with 3MPS were synthesized as previously reported [9]. Briefly, starting with 200 mg (5 × 10−<sup>4</sup> mol) of HAuCl4 × 3H2O in 20 mL of deionized water, a solution of 3MPS in 20 mL of deionized water was added under vigorous stirring (Au/S = 1/4 molar ratios). Two hours after the addition of the reduction agen<sup>t</sup> (a water solution of NaBH4, Au/NaBH4 molar ratio = 1/10), a solid black product was isolated and purified by centrifugation (13,000 rpm, 20 min, five times with deionized water). AuNP main characterizations: UV–Vis (λmax (nm), H2O) 523 nm; DLS (<2R H> (nm), H2O): 12 ± 3 nm; Z potential: –35 ± 3 mV; FESEM (nm) 8–10 nm. Complexes A and B were prepared according to procedures reported in the literature [45,50]. They showed a well-known UV–Vis spectrum, as reported in the Supporting Information, Figures S1a,b). The conjugate nanoparticles were prepared using the following procedure. The AuNPs and A were mixed in water (Au/A = 5/1 w/w) under gentle stirring (room temperature, 4 h) and then the suspension was centrifuged (13,000 rpm, 2 h) to obtain AuNPs-A as a solid residue. It was lyophilized and stored at room temperature, while the supernatant was used for loading evaluations. The AuNPs and B were mixed in MeOH (Au/B= 5/1 w/w) under gentle stirring (room temperature, 4 h) and then the suspension was centrifuged (13,000 rpm, 30 min) to obtain AuNPs-B as a solid residue. It was lyophilized and stored at room temperature, while the supernatant was used for loading evaluations. The loading and the loading efficiency (η) were calculated by using calibration curves, as reported in the Supporting Information (Figures S1c,d) and calculated in reference to our previous work [9]. For each sample, three independent measurements were carried out and the mean value and standard deviation are reported.

### *2.3. Stability and Release Studies*

For the stability studies, AuNPs-A and AuNPs-B were dispersed in water at the concentration of 0.1 mg/mL and the size of nanoparticles was measured over 10 days at room temperature. The release studies were performed in H2O at 37 ◦C over 4 days, using 2 mg of conjugated nanoparticles in 20 mL of media. The released was calculated by analyzing the water solution and detecting the free complex by using UV–Vis measurements, in reference to our previous work [9]. For each sample, three independent measurements were carried out and the mean value and standard deviation are reported.
