4.2. Synthesis of Bulk-Hydrogel

The hydrogels used here were synthesized by UV free radical polymerization using poly(ethylene glycol) diacrylate (PEGDA, 700 Da) at different concentrations in Milli-Q water and DAROCUR 1173 used as initiator [57]. Each hydrogel sample was prepared dissolving photoinitiator in 10 mL of polymer solution, obtaining an initiator final concentration of ~0.1% v/v. The reaction mixture was strongly mixed and then purged with high purity nitrogen for 5 min to remove the excess of oxygen that may interfere with the free radical polymerization. The reaction mixture was then carried out in 10 mL test tubes and illuminated with UV lamp (λ = 365 nm and power-lamp = 10 W) for 5 min leading to complete polymerization. For NMR studies, we reduced the total reaction volume to 1 mL of deuterated water. Polymerization was performed directly in special NMR tubes designed for gel samples. Hydrogel samples were than expelled from the NMR tube and put in a solution of D₂O for the next 24 h to remove all the unreacted materials. Hydrogels were dried in oven at 30 °C for few hours, swelled with 1 mL of probe solution and finally put in the NMR tube for the measurement. Different probes, sulforhodamine G and several dextrans (3 KDa, 10 KDa and 40 KDa) were dissolved in D₂O to reach a final concentration of 1 mg/mL. Moreover, functionalized bulk were synthesized using UV free radical photopolymerization between PEGDA and oligonucleotide, properly modified with methacrylamide moieties. Propagation step of the reaction between polymer and methacrylate oligonucleotide is highlighted in Figure 1b*.

Several recipes with different PEGDA and oligonucleotide concentrations were prepared and tested. The mixture was composed of PEGDA (MW 700 Da) at different concentrations (10–15–20% w/v) in buffer solution, DAROCUR 1173 as initiator and fluorescent oligonucleotide methacrylate (F-DNA-Tail) at different concentrations (1–5 μM). Our buffer solution was obtained adding 1 × PBS and NaCl 200 mM in Milli-Q water. The reaction mixture was strongly mixed and then purged with high purity nitrogen for 5 min to remove the excess of oxygen that may interfere with the free radical polymerization. Then, 100 μL of the mixture was carried out in 96-optiplate, illuminated with the same UV lamp used before, for 5 min leading to complete polymerization.