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As a first step for the development of biosensing inks for inexpensive paper-based biodetection, we prepared paper strips printed with carboxylic poly( N-isopropylacrylamide) microgels that were modified either with an antibody or with a DNA aptamer. We found that the antibody and the DNA aptamer retained their recognition capabilities when coupled to microgel. The printed microgel remains stationary during chromatographic elution while the microgel-supported molecular recognition elements are accessible to their intended targets present in the elution solution. Our work indicates that microgels, large enough to isolate the biosensors from the paper surface, are sufficiently hydrophilic to be wetted during chromatographic elution, exposing the gel-supported affinity probes to their targets.

Regenerated cellulose films were laminated using very thin layers of the protein Bovine Serum Albumin (BSA) as an adhesive. The wet delamination strength was measured as functions of pH, lamination time, temperature and pressure, as well as cellulose oxidation. Drying at elevated temperature (120 °C) was required for strong adhesion. Oxidation of the cellulose membranes to introduce surface carboxyl/aldehyde groups increased the wet delamination strength by 60%, implying that the peel failures happened at the protein/cellulose interface. The wet delamination force was independent of the pH and ionic strength of solutions used to apply the BSA; whereas adhesion decreased with increasing pH of the rewetting solution. Furthermore, the swelling of the BSA interplay region was also increased at high pH. It is proposed that covalent grafting of BSA onto the oxidized cellulose, and disulfide crosslinking within the protein layer contributed to wet adhesion.

The initiation and propagation reactions in anionic non-equilibrium polymerization of octamethylcyclotetrasiloxane (D4) initiated by silazyl-lithiums are investigated. It is found that: both the steric hindrance effect and the electronic effect of the substitutes on the Si atom Si influences the initiation activity of silazyl-lithiums; temperature effect on the propagation rate of D4 increases strongly above 40 °C; the molecular weight distribution of the prepared polysiloxanes widens with time. © 2003 Society of Chemical Industry

A new kind of polytitanosilazane (PTSZ) precursor for Si/C/N/Ti-based ceramic was synthesized from the condensation reaction of silazane lithium salts and titanium tetrachloride (TiCl4). Titanium in the precursors was bonded to silazane compounds in the Si—N—Ti bond. The obtained PTSZs were characterized by Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), and elemental analyses. The PTSZs were pyrolyzed at 900 to 1300°C under nitrogen, argon, and ammonia atmosphere, respectively, to give amorphous inorganic products. The results indicated that ceramic yields of PTSZs were much higher than that of their corresponding silazane oligomers and ceramic yields increased with the increase in Ti content in PTSZs. Precursors containing reactive vinyl groups gave higher pyrolytic yields. The pyrolytic yield under ammonia is lower than that under nitrogen and argon. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2733–2739, 2004

With the long-term goal of developing paper surfaces that will detect pathogens, we have investigated physical adsorption and covalent coupling as strategies for treating cellulose surfaces with a DNA aptamer that binds ATP. Physical adsorption was reversible and the isotherms fitted the Langmuir equation with an adsorption maximum of 0.105 mg/m2 at high ionic strength (300 mM NaCl, 25 mM Tris-HCl) and only 0.024 mg/m2 in lower ionic strength buffer (25 mM Tris-HCl). Covalent coupling of amine-terminated aptamer with oxidized cellulose film (Schiff base + reduction) gave 25% coupling efficiency while maintaining the aptamer activity which was illustrated by using a known fluorescent aptamer that is capable of ATP detection. Therefore, covalent coupling, without spacer molecules, is a promising approach for supporting biosensing aptamers on cellulose.

We demonstrate that DNA oligonucleotides covalently coupled to colloidal microgel can be manipulated by T4 DNA ligase for DNA ligation and by Phi29 DNA polymerase for rolling circle amplification (RCA). We also show that the long single-stranded RCA product can generate intensive fluorescence upon hybridization with complementary fluorescent DNA probe. We believe DNA-microgel conjugates can be explored for the development of DNA based bioassays and biosensors.