## 3 Results and Discussion
### On-Chip Polysome Capture and RNA Purification
mRNA obtained after the elution process was 73% of the initial amount for the silanized microdevice and 56% for the untreated microdevice. Beside the amount of RNA adsorbed and eluted, the quality and integrity of the recovered RNA is crucial for further analyses. Results of capillary electrophoresis analysis (Figure 3B,C) show that RNA extracted from the silanized microdevices (solid line, panel B) is mainly composed by peaks identified with ribosomal and polysomal intact RNAs. On the contrary, in the case of the untreated microdevice (solid line, panel C), the RNA is composed mainly by shorter fragments, indicating a large degree of degradation, possibly due to the interaction with the bare surfaces. In fact, the presence of intact rRNA 18S and 28S, around 2000 and 5000 nt, respectively, is clearly visible in fractions eluted from the functionalized microdevice and not in fractions eluted from the untreated microdevice, confirming better performances in the first case. The unbound RNA (dashed line, panel B and C) is in both cases a minimal amount. These results confirm those results obtained with TG-SO plane surfaces functionalized with triCAS. These surfaces in fact immobilized the highest number of polysomes per cm\({}^{2}\) among the tested surfaces, without introducing a noticeable degradation (Table 6 and Figure 2). The proof-of-concept of polysomes entrapment was performed with prepurified polysomes in order to compare protocols set up for plane surfaces and since the results were confirmed, a further proof-of-concept was performed starting from cell lysate. In this case, the protocol was slightly modified by introducing a washing step aimed at removing all the unwanted material other than polysomes, prior to elute RNAs. The eluted material was then analyzed by capillary electrophoresis and a comparison between RNA eluted from functionalized and nonfunctionalized microdevices was performed (Figure S10). As clearly visible, the RNA eluted both from functionalized and from nonfunctionalized microdevices is mainly constituted by mRNA, while no rRNA is present. However, about six times more mRNA is recovered from the functionalized microdevice with respect to the nonfunctionalized microdevice. Therefore, the protocol set up for prepurified polysomes is able to entrap polysomes from cell lysate and could be utilized for the elution of mRNA associated with polysomes. Even if a deeper investigation is certainly required before suggesting the use of these microdevices as diagnostic tools (for example, to identify alterations in protein synthesis leading to altered mRNA profiles or expression), the proof-of-concept here presented represents a very appealing and potentially breakthrough approach for rapid and integrated analyses of polysomally associated mRNA on a single monolithic microdevice with clear impact in hands-on diagnostics and biomarker discovery. Figure 3: RNA recovery from silicon/Pyrex microdevices functionalized with triCAS or untreated. Panel A: RiboGreen quantification; panel B: electropherograms of RNA unbound and eluted from microdevices functionalized with triCAS; panel C: electropherograms of RNA unbound and eluted from untreated microdevices.