Carboxymethylated Dextran-Modified N-Heterocyclic Carbene Self-Assembled Monolayers on Gold for Use in Surface Plasmon Resonance Biosensing

Abstract

Surface chemistry is a key enabler for various biosensing applications. Biosensors based on surface plasmon resonance routinely employ thiol-based chemistry for the linker layer between gold-coated support surfaces and functional biosensor surfaces. However, there is a growing awareness that such sensor surfaces are prone to oxidation/degradation problems in the presence of oxygen, and previous efforts to improve the stability have shown limited advancements. As an alternative, recent studies employing N-heterocyclic carbene (NHC) self-assembled monolayers (SAMs) deposited on gold have shown significant promise in this area. Here, we describe a sensor surface employing an NHC SAM to couple a modified carboxymethylated dextran onto a gold surface. Such a dextran matrix is also used for affinity chromatography, and it is the most commonly employed matrix for commercial biosensor surfaces today. The performance reliability of the dextran-modified NHC chip to act as an alternative biosensing platform is compared with that of a thiol-based commercial chip in the proof-of-concept tests. The resultant NHC sensor surface shows a higher thermal stability compared to thiol analogues. Moreover, the plasma protein/drug and antibody/antigen interactions were validated on the NHC-based dextran chip and showed similar performance as compared to the thiol-based commercial chip. Ultimately, this study shows the strong potential applicability of chemical modifications to gold surfaces using NHC ligands for biosensing applications.

Electrochemical deposition of N-heterocyclic carbene monolayers on metal surfaces

“…Thus far, NHC-based SAMs have been mostly prepared on metallic surfaces, and specifically on Au surfaces, by two approaches: (i) base-induced deprotonation of imidazolium salt precursors 5 , 7 , 17 , 26 , 34 and (ii) annealing of NHC(H)[HCO 3 ] salts 10 , 13 , 15 , 21 or NHC–CO 2 adducts 5 , 11 , 14 , 15 under vacuum conditions (Fig. 1 ).…”

“…The strong NHC-metal interaction enabled the formation of stable self-assembled monolayers (SAMs) of NHCs on metals [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] , metal-oxides 22,23 and semimetals 24 . The wide chemical-tunability of NHCs led to utilization of NHC-based SAMs as biosensors 10,25,26 , molecular probes for surface reactivity [27][28][29] , and co-catalysts 3,[30][31][32][33] .…”

“…1). The deposition process of imidazolium salt precursors with halide ions (Cl − , Br − , I − ) is conducted in THF under an anhydrous environment with a strong base, such as potassium tert-butoxide (KO t Bu), for deprotonation and carbene formation 5,7,17,26 . Although this deposition approach has been widely utilized for the preparation of NHC-based SAMs, it has a number of inherent drawbacks: First, an anhydrous environment is required since residual water can quench the active carbene.…”

Electrochemical Deposition of Addressable N-Heterocyclic Carbene Monolayers

“…[1][2][3] The strong NHC-metal interaction enabled the formation of stable and chemically-addressable self-assembled monolayers (SAMs) of NHCs on metals, [4][5][6][7][8][9][10][11][12][13][14][15][16] metal-oxides 17,18 and semimetals. 19 The wide chemical-tunability of NHCs led to utilization of NHC-based SAMs as biosensors, [20][21][22] molecular probes for surface reactivity [23][24][25] and co-catalysts. 2,[26][27][28][29] NHC-based SAMs have been prepared thus far by two deposition techniques; namely liquid-and vapor-phase deposition (Scheme 1a and 1b, respectively).…”

Electrochemical Deposition of Addressable N-Heterocyclic Carbene Monolayers

“…[1][2][3] The strong NHC-metal interaction enabled the formation of stable and chemically-addressable self-assembled monolayers (SAMs) of NHCs on metals, [4][5][6][7][8][9][10][11][12][13][14][15][16] metal-oxides 17,18 and semimetals. 19 The wide chemical-tunability of NHCs led to utilization of NHC-based SAMs as biosensors, [20][21][22] molecular probes for surface reactivity [23][24][25] and co-catalysts. 2,[26][27][28][29] NHC-based SAMs have been prepared thus far by two deposition techniques; namely liquid-and vapor-phase deposition (Scheme 1a and 1b, respectively).…”