Acoustic biosensor for discrimination of pathogens according to Gram-principle

The microacoustic methods of biomedical analysis, implemented on piezoelectric crystals and ceramics are becoming increasingly perspective due to potential of integration, as functional elements of biosensors. An important stage in diagnostics of infectious diseases is the identification of pathogens. One of possible applications of such sensor is an alternative to time and labor consuming Gram method of discriminating bacteria according to composition of their cell walls. Thus, bacteria which in a procedure of Gram staining, do not decolored after application of dye solution, are classified as Gram-positive (G(+)). They are surrounded with the thick peptidoglycan layer, pulpy and dampening acoustic waves. While Gram-negative (G(–)) bacteria, which acquire red color in Gram procedure, are covered with thin and springy layer, demonstrating resonance effects when interact with acoustic fields. Thus, G(+) and G(–), which differently colored in Gram procedure are also react differently to external acoustic field: for G(–) bacteria, this is a sharp decrease in the Q-factor of the "resonator-suspension" system and a shift of the resonance curve to lower frequencies. While for G(+) bacteria, although a certain shift of the resonance curve was also observed, but the bandwidth of resonance curve practically did not change. This effect was studied for L. acidophilus (G(+)) and E. coli (G(–)) bacilli with quarts resonators of 4 MHz, 5 MHz and 10 MHz. The biosensor was testing using Lactobacillus fermentum, E. coli M-17, Bifidobacterium bifidum, Burkholderia cepacia, Staphylococcus aureus. At this stage it has been demonstrated that the method is particularly effective for discriminating bacteria of the similar size, such as, for example cocci. The discrimination of Gram factor for cocci and bacilli was less accurate and needs further studies for selection of precise resonance frequencies.