Preparation of porous polymer monoliths featuring enhanced surface coverage with gold nanoparticles

Abstract

A new approach to the preparation of porous polymer monoliths with enhanced coverage of pore surface with gold nanoparticles has been developed. First, a generic poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith was reacted with cystamine followed by the cleavage of its disulfide bonds with tris(2-carboxylethyl)phosphine, which liberated the desired thiol groups. Dispersions of gold nanoparticles with sizes varying from 5 to 40 nm were then pumped through the functionalized monoliths. The materials were then analyzed using both energy dispersive X-ray spectroscopy and thermogravimetric analysis. We found that the quantity of attached gold was dependent on the size of nanoparticles, with the maximum attachment of more than 60 wt% being achieved with 40 nm nanoparticles. Scanning electron micrographs of the cross sections of all the monoliths revealed the formation of a non-aggregated, homogenous monolayer of nanoparticles. The surface of the bound gold was functionalized with 1-octanethiol and 1-octadecanethiol, and these monolithic columns were used successfully for the separations of proteins in reversed phase mode. The best separations were obtained using monoliths modified with 15, 20, and 30 nm nanoparticles since these sizes produced the most dense coverage of pore surface with gold.

Fig. 1

Preparation of poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith and its modifications with cystamine, reduction with tris(2-carboxylethyl)phosphine, attachment of gold nanoparticles, and coating with 1-octanethiol.

Fig. 2

Energy dispersive X-ray spectroscopy data for generic poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith (a), after modification with cystamine (b), and after reduction with tris(2-carboxylethyl)phosphine (c).

Fig. 3

Scanning electron micrographs of the internal structures of poly(glycidyl methacrylate-co-ethylene dimethacrylate) monoliths with attached 5 (a), and 10 nm (b) gold nanoparticles, taken using InLens detector and 1 kV power source.

Fig. 4

Scanning electron micrographs of the internal structures of the poly(glycidyl methacrylate-co-ethylene dimethacrylate) monoliths with attached 15 (a), 20 (b), 30 (c), and 40 nm (d) gold nanoparticles, taken SE2 detector and 2 kV power source.

Fig. 5

Scanning electron micrograph of the internal structure of the poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith with attached 40 nm gold nanoparticles and coated with ca. 10 nm thick carbon layer taken using SE2 detector and 2 kV power source.

Fig. 6

Resistance to flow expressed as the back pressure normalized to 1 m column length measured for the generic poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolithic column and for the same column after modification with cystamine, reduction with tris(2-carboxylethyl)phosphine, attachment of 15 nm gold nanoparticles, and functionalization with 1-octanethiol and 1-octadecanethiolConditions: Mobile phase 20 vol% acetonitrile in water, flow rate 1 μL/min.

Fig. 7

Reversed-phase separation of proteins using monolithic columns. Conditions: Columns: generic 116 mm × 100 μm I.D. (a), cystamine modified 119 mm × 100 μm I.D. (b), and with attached 15 nm gold nanoparticles 117 mm × 100 μm I.D. (c); mobile phase: A 0.1% aqueous trifluoroacetic acid, B 0.1% trifluoroacetic acid in acetonitrile, gradient from 20 to 70% B in A in 20 min, flow rate 1.0 μL/min, injection volume 10 nL, UV detection at 210 nm. Peaks in (a): impurity from ribonuclease A (1), ribonuclease A (2), cytochrome C (3), myoglobin (4).

Fig. 8

Reversed-phase separation of proteins using monolithic columns containing gold nanoparticles modified with 1-octanethiol. Conditions: Columns: 5 nm GNP 100 mm × 100 μm I.D. (a), 10 nm GNP 110 mm × 100 μm I.D. (b), 15 nm GNP 110 mm × 100 μm I.D. (c), 20 nm GNP 108 mm × 100 μm I.D. (d), 30 nm GNP 80 mm × 100 μm I.D. (e), and 40 nm GNP 89 mm × 100 μm I.D. (f), mobile phase: A 0.1% aqueous trifluoroacetic acid, B 0.1% trifluoroacetic acid in acetonitrile, gradient from 20 to 70% B in A in 20 min, flow rate 1.0 μL/min, injection volume 10 nL, UV detection at 210 nm. Peaks: impurity from ribonuclease A (1), ribonuclease A (2), cytochrome C (3), myoglobin (4).

Fig. 9

Reversed-phase separation of proteins using monolithic column containing 15 nm gold nanoparticles modified with 1-octadecanethiol. Conditions: Column: 89 mm × 100 μm I.D., mobile phase: A 0.1% aqueous trifluoroacetic acid, B 0.1% trifluoroacetic acid in acetonitrile, gradient from 20 to 70% B in A in 20 min, flow rate 1.0 μL/min, injection volume 10 nL, UV detection at 210 nm. Peaks: impurity from ribonuclease A (1), ribonuclease A (2), cytochrome C (3), myoglobin (4).