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Facile Functionalization of Polymer Surfaces in Aqueous and Polar Organic Solvents via 3‑Mercaptopropylsilatrane Yen-Ta Tseng,† Hsin-Yu Lu,§ Jie-Ren Li,§ Wan-Ju Tung,† Wen-Hao Chen,† and Lai-Kwan Chau*,†,‡ †
Department of Chemistry and Biochemistry and ‡Center for Nano Bio-Detection (AIM-HI), National Chung Cheng University, Chiayi County 62102, Taiwan § Department of Chemistry, National Cheng-Kung University, Tainan City 70101, Taiwan S Supporting Information *
ABSTRACT: Surface modification of a polymer substrate with a mercapto functionality is crucial in many applications such as flexible circuitry and point-of-care biosensors. We present here a novel bifunctional molecular adhesive, 3mercaptopropylsilatrane (MPS), as an interface between polymer and metal surfaces. Under ambient conditions, surface modification of polymer surfaces with a mercapto functionality can be achieved with low concentration (0.46 mM) of MPS in aqueous solvent (50% ethanol) in a short time ( PC > PMMA > PET. Anchoring Gold Nanoparticles and Silver Nanoparticles. As LSPR sensors are mostly based on gold
Figure 5. (A) Absorbance at 520 nm versus immersion time for MPSmodified polymer (PC, PET, PMMA) and glass slides with each set of slides immersed separately into an MPS solution and then immersed in a AuNP solution. (B) FE-SEM images of AuNPs on the surface of (I) PC, (II) PET, and (III) PMMA with an MPS deposition time of 20 min and subsequent AuNP deposition time of 15 min for all cases.
nanoparticles (AuNPs), and to a smaller extent, silver nanoparticles (AgNPs), how to optimize the amount and distribution of these nanoparticles on MPS-treated polymer substrates is an important issue. In this regard, the absorbance and fwhm of the plasmon band are important parameters for optimization of LSPR sensors. Here, we mainly use AuNPs to evaluate the characteristics of the nanoparticles on MPS-treated PC, PET, and PMMA substrates. As shown in Figure 5, the saturated coverages of AuNPs on all three polymer surfaces are similar but are slightly lower than that on glass, while the fwhm of the plasmon bands are typically between 86 and 96 nm, which is similar to that of AuNP-modified glass slides (see Figure S3 of the Supporting Information). We also evaluate the feasibility of immobilization of AgNPs on a polymer surface. As shown in Figure S4 of the Supporting Information, AgNPs are successfully immobilized on a PMMA slide with an fwhm of 80 nm, which is slightly wider than that of an AgNP-modified glass slide (fwhm = 66 nm). The comparable plasmon bands of AuNPs and AgNPs on polymer substrates with those on corresponding glass substrates suggests that MPS potentially can play a role in the development of polymer-based LSPR sensors. Reaction Mechanism Proposed. In order for MPS to deposit on a polymer surface, surface hydroxyl and carboxyl group are possible reaction sites. Obviously, among the four surfaces, the glass surface has the highest density of surface hydroxyl groups and thus exhibits the highest deposition rate. For PC, oxidation of the PC surface under oxygen plasma results in more polar hydroxyl groups.34,47 Condensation between C−OH on the PC surface and Si−OH on MPS may then take place.48 PMMA is more sensitive to oxygen plasma than PC due to the absence of aromatic rings in the backbone.47 It has been proposed that oxidation of the F
DOI: 10.1021/acsami.6b13926 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
ACS Applied Materials & Interfaces
Figure 6. Schematic of the formation of an MPS film on a polymer surface with few reactive sites.
Figure 7. Adsorption of AuNPs onto an MPS-modified PC slide viewed for 10 × 10 μm2 AFM topography and zoom-in (1 × 1 μm2) view image: (A) Untreated PC surface; (B) MPS-modified PC slide; and (C) AuNPs adsorbed onto the MPS-modified PC slide. Blue arrows in (A) indicate nanosized domains of the PC surface. Red arrows in (B) show MPS aggregates. Green arrows in (C) exhibit AuNPs.
PMMA surface under oxygen plasma results in terminal carboxylic acid groups.35 The electronegativity difference between a carboxyl group and a silanol group is the driving force toward the formation of the Si−O−C bond.49 For PET under oxygen plasma, it has been proposed that a surface activation reaction is initiated by hydrogen abstraction from the methylene groups with oxygen diradicals, resulting in the
formation of terminal carboxyl groups as well as hydroxyl groups.33 A previous report based on hydrolysis of PET indicates that the number of −OH and −COOH groups per PET repeat unit is
