Fig. 1. (A) Plots of PHEMA film thicknesses as a function of polymerization time on ATRP-initiator-coupled ethanethiol-coated substrates that were () protected by N₂ purge, (♦) without purge but added with 690 mM Cu(0) as the reducing agent, and (■) without purge nor Cu(0) addition. (B) A plot of polymer film thicknesses as a function of the amount of copper powder added in the reaction mixture after 2-h purge-free ATRP. The error bars corresponded to the standard deviation of five measurements at each time point. Note that at some points the error bars were too small to be seen. Experimental conditions: all substrates were coated with ATRP-initiator-coupled ethanethiol; CuCl:CuBr₂:bpy = 1:0.3:3 (molar ratio), [CuCl] = 69 mM, HEMA:H₂O = 1:1 (v/v). Other conditions see the text.

Fig. 2. (A) Plots of PHEMA film thickness on ssDNA-coated surfaces as a function of polymerization time. The unpurged solution (♦) contained Cu(0):CuCl:CuBr₂:bpy = 10:1:0.3:3 (molar ratio), whereas the purged system () had only CuCl:CuBr₂:bpy = 1:0.3:3. (B) A plot of the thicknesses of PHEMA as a function of the concentration of the target DNA molecules (C′D′). The error bars corresponded to the standard deviation of five measurements at each time point. Note that at 1 fM point the error bar was too small to be seen. For the two control experiments, one surface was coated with a non-complementary capture probe (NC) and exposed to a 1-μM target DNA solution, and the other was coated with the complementary capture probe (C) but incubated with a solution without the target DNA molecules. Experimental conditions: Au substrates were coated with complementary capture probe (C) unless specified; DNA hybridization = 1 h, ATRP initiator-coupled detection probe D = 1 μM, T4 ligation = 2 h, Cu(0):CuCl:CuBr₂:bpy = 10:1:0.3:3 (molar ratio), [CuCl] = 69 mM, HEMA:H₂O = 1:1 (v/v), ATRP reaction time = 2 h.

Scheme 1. General mechanism of purge-free ATRP using Cu(0) as the reducing agent.