Similar to atomic force microscopy rupture event

Similar to atomic force microscopy, rupture event scanning does not involve electromagnetic radiation. We record the excitation of oscillations caused by the rupture of bonds between the particle and the surface. The signal not only points to the presence of the particles on the surface but also indicates the number of particles and their affinity to the receptor attached to the surface. Scanning process requires minimal sample preparation, can be carried out in different environments (in vacuum, in the air, or in liquid), and takes only a few minutes. The working range for the method proposed by us is 108–109 DNA molecules; this is quite comparable with the value reported in [3] for the electrochemical DNA sensor: 10−15M, which is 6·108 molecules. In our experiments, the number of DNA purchase gap-26 on the QCM surface (1mm2) was about 108, so that surface coverage with DNA molecules was 1% or lower. However, using a flow system, it is possible to achieve DNA accumulation on the surface by passing a solution with low concentration. Another important feature is that our method not only detects the rupture of DNA from the surface but also measures binding forces and allows studying the dependence of binding force on external action, for example on pH or salt concentration. This method provides the ground for the development of the new sensor type measuring the forces of affine interactions in biological systems using the surface of sensor element. Experiments with model DNA samples showed that this method can be the basis for the rapid analysis of nucleic acids.
Materials and methods
Results and discussion The principle of the proposed sensor was illustrated with a model system. Oligomer ON1 was attached to the modified surface; a complementary oligonucleotide ON2 or non-complementary one was then applied on the surface (Fig. 2). The addition of the complementary pair (which would result in formation of the double helix) resulted in a rupture signal at 3V. In contrast, after the addition of a non-complementary oligomer, the signal appeared at 0.8V. The positions of the signals for other oligonucleotides can be different, depending on bonding force and molecular mass. In our case the molecular masses of complementary and non-complementary oligonucleotides were identical.
Conclusion The sensitivity of the method allows reliable operation using solutions with the concentration about 109molecules/mm2. Unwinding of DNA molecule occurs not due to inertia forces as it was the case for the detachment of large particles (>150nm), but due to the gradient of velocities in the fluid, resulting from the harmonic oscillations of the QCM surface. In the present work we carried out the direct measurement of the force of bond unwinding in the double DNA helix. The results confirmed that the force of bonding in the double helix of DNA under investigation is 30–40pN. This procedure provides the ground for the development of new types of sensors measuring the force of affine interactions (probe/biomolecular target) on the surface of the sensor element. Experiments carried out with the model DNA showed that this procedure could form the basis for rapid nucleic acid testing.
Conflict of interest
Acknowledgements This work was supported by SB RAS Integration Project No. 86.2, and by the Ministry of Education and Science of the Russian Federation.
Introduction Melamine (2,4,6-triamino-1,3,5-triazine) is a kind of triazine analogue together with three amino groups (pKa=5.1). Melamine tends to hydrolyse under strong acid or alkali conditions resulting in the formation of cyanuric acid (2,4,6-trihydroxy-1,3,5-triazine), ammeline (4,6-diamino-2-hydroxy-1,3,5-triazine) and ammelide (6-amino-2,4-dihydroxy-1,3,5-triazine) [1–4]. It has a chemical compound that has been industrially used to synthesise melamine–formaldehyde resins (MFR) for the production of laminates, glues, dinnerware, adhesives, moulding compounds, coatings, as well as flame-retardant materials since 1950s [5].