TA-polyallylamine

The adsorption curve of DNA-conjugated TA-polyallylamine in pH 8.0 equilibration buffer indicated that the surface plasmon resonance (SPR) response was only slightly reversed by washing with buffer (Fig. 6A, curve I). 

This result shows that DNA-conjugated TA-polyallylamine can be immobilized on a surface via self-assembly. To verify that this result is due to self-assembly, DNA-conjugated TA-polyallylamine lacking TA side chains was used as a control. This polymer was also retained on the surface after washing (Fig. 6A, curve II) the residual response (1900 response unit (RU)) was probably due to nonspecific interaction between the DNA side chains of the polymer and the gold surface of the sensor. However, the amount of bound polymer was less than that for the DNA-conjugated TA-polyallylamine. The SPR response in the presence of polyallylamine alone (without DNA) was low (only 780 RU) after washing (Fig. 6A, curve III). 

The DNA-conjugated TA-polyallylamine-immobilized substrate was tested to determine its ability to recognize fully matched DNA. First, unmatched DNA (20. ig mb1) was injected onto the DNA-conjugated TA-polyallylamine-immobilized substrate. Then, after washing with equilibration buffer continuously, fully matched DNA (20 igmf 1) was injected onto the DNA-conjugated TA-polyallylamine-immobilized substrate. The response of this probe to fully matched DNA was much higher than its response to unmatched DNA (Fig. 6B). 

The effect of pH on the hybridization selectivity of the DNA-conjugated TA-polyallylamine-immobilized substrate was studied. At pH 8.0 and 10, the... 

The hybridization selectivity and efficiency of DNA-conjugated PDPH-PAA were investigated with 1 pg mL 1 of injected sample DNA. The response to fully matched DNA (89 RU) was equivalent to 0.92 pmol cm 2, which indicates a hybridization efficiency of 33%, based on the amount of probe DNA on the surface (2.8 pmol cm 2). This hybridization efficiency was lower than that of DNA-conjugated TA-polyallylamine however, for DNA-conjugated TA- polyallylamine and PDPH-PAA, the maximum response when 1 pgmL-1 of unmatched DNA sample was injected decreased from 94 RU to 21 RU. These results suggest that less nonspecific DNA adsorption occurs with DNA-conjugated PDPH-PAA due to the electrostatic repulsion between the car-... 

Fig. 10 SPR responses of DNA-conjugated polymers to fully matched and unmatched DNA. The sensor consisted of (A) DNA-conjugated TA-polyallylamine immobilized on the gold substrate or (B) DNA-conjugated PDPH-PAA immobilized on the substrate. Curves I and III fully matched DNA curves II and IV unmatched DNA. DNA-conjugated polymer was immobilized on substrate for 24h. SPR responses were normalized with respect to maximum signal observed for fully matched DNA...

DNA-conjugated polymers were prepared from polyallylamine or polyacrylic acid (PAA) modified with ssDNA as a probe, and thioctic acid (TA) or 3-(pyridyldithio)propionyl hydrazide (PDPH) for self-assembled immobilization. The oligonucleotides sequences of the probes and of the fully matched and unmatched DNAs were S -TCC-TCT-TCA-TCC-TGC-TGC-TAT-GCC-TCA-TCT-T-R, 5 -AGA-TGA-GGC-ATA-GCA-GCA-GGA-TGA-AGA-GGA-3, ... 

The amino group of polyallylamine (Mw 70 000) is covalently modified with TA for self-assembly immobilization and NHS-ester-linked ssDNA as the probe. The chemical structure of the polymer unit is shown in Fig. 5. The amounts of ssDNA and TA in the polymer were determined to be equivalent to 1/424 [molecule/monomerunit] and 1/42 [molecule/monomerunit], respectively, by absorption measurements. 

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