From an anlytical biochemistry perspective it opens the prospect of being able to discriminate between close chemical analogues that would be unobservable with a tool such as Mass Spectroscopy. that this gold standard is very much not real time, masks will be combined in this paper with the notions of in-phase (I) and quadrature (Q) signals from digital radio to manifest an approach to molecular recognition that allows a level of discrimination and analysis unobtainable without the aggregate. As an example we present experimental data on the detection of TNT, RDX, C4, ammonium nitrate and musk oil from a system of antibody-coated acoustic wave sensors. component of systems biology. Our specific work and data are most directly related to the vapor phase detection of nitrous oxide-based Isradipine explosives using surface acoustic wave (SAW) biosensors. Though ours is an ex vivo system we believe that our findings cast light on the intricacies of molecular recognition. Almost every biomolecular event in living systems involves the following three principle components: Molecular recognition—the lock and key interaction whereby one biomolecule or receptor (e.g. a protein) Isradipine recognizes with a high degree of specificity another molecule. In the case of electrophysiology, this extends to the recognition of an ion, say Na+, by a channel protein which has been incorporated into the plasma membrane Conformational change—the change in the molecular structure of the receptor molecule. At times it helps to think of this as the phase change of the Isradipine molecule. No additional chemical groups have been added to the molecule but the internal structure of the molecule has changed. Condensed matter physics is replete with examples of crystal structure radically affecting macroscopic physical characteristics The hydrolysis of nucleotide triphosphates (ATP, GTP, UTP and CTP) as an energy source. As we have made known in our previous publications[13C15], acoustic wave biosensors are a technology well suited for the translation of the above first two principles of the canon of living systems into detectable electrical signals. These two principles of conformational change and molecular recognition are introduced in the abstract of this paper. Combined, these principles manifest themselves as mass attachment to the sensor surface and stiffness changes in the biological receptor layer. These in turn will shift the resonant frequency of the device (e.g. 10MHz for a QCM or quartz crystal microbalance or 250 MHz for a SAW resonator based oscillator). The biological receptor layer can, and has, taken on many forms such as aptamers, peptides among others. It should be understood that though much of what is presented in this paper directly references antibodies, the work can easily be extrapolated in general to other molecular recognition elements (MRE). The affinity of the antibody immobilized onto the surface of the acoustic wave device will alter the time course of the resonant frequency signature, into an electrical signal. The fundamental starting point of this analysis will be the frequency signatures, antibody layer and/or other biomolecules, GNG12 Hunt is the acoustic velocity; is the density of the film; is the thickness of the film; and are the shear stiffness and density of the quartz crystal, respectively; is the stiffness of the film; is the difference between perturbed and unperturbed (denoted by subscript is mapped into an IQ constellation diagram. 3. Experimental Methodology and Results Initially, we will discuss the vapor phase Isradipine biosensor detection system configuration in which there are two antibody coated SAW sensors and one reference sensor. To introduce the analogy with digital radio, we will speak of these antibody-coated sensors as channels. Each channel consists of an orthogonal or semi-orthogonal SAW immunosensor shown previously in Fig. 1[25]. This orthogonal biosensor detection system is illustrated in Fig. 2A where the X channel output is from oscillator X implementing the SAW immunosensor coated with biolayer X and the Y channel output is from oscillator Y implementing the SAW immunosensor coated with biolayer Y. Open in a separate window Figure 2. A schematic of 2-channel (A), and n-channel (B) biosensor system Figure 3A illustrates the domain conversion technique where each separate time-frequency characteristic of the X and Y oscillators are mapped onto a single quadrature frequency domain, with both axes having the units of Hz. The sampling of the time-frequency characteristics can be strategically controlled depending on the system parameters such as the time duration of the analyte injection. Open in a separate window Figure 3. (A) Conversion from Isradipine time-frequency domain to the quadrature phase domain. (B) 8-ary QAM constellation diagram. (C) two channel immunosensor signal state-space map There is a strong analogy between the detection techniques of a quadrature digital communication system and that of our orthogonal.