The LOD of SERS-based aptasensor was estimated to be 7•10−5–1.3•10−4 HAU per sample or 1•104–2•104 virus particles per sample. It is 101 to 103 times lower than most values published for other aptamer-based approaches for the virus, i.e. 10−1 to 10−3 HAU. The only aptamer-based technique with the lowest LOD was described by Kiilerich-Pedersen et al.
The LOD was as low as 2 pfu/probe, which is ≈ 2•102 virus particles per sample (recalculation was made using data from Kramberger et al. The technique detected subtle changes in the impedance of the microelectrode in a microfluidic channel.
As for non-aptamer SERS-based techniques, detection of influenza genome via complementary DNA probe was shown to have no advantages in terms of LOD having sensitivity 2.7 attomole of RNA per probe (nearly 1.5•105 virus particles per sample). SERS-based lateral flow immunoassay had 10-fold higher LOD as tested for H7N9 influenza virus.
As compared to common laboratory techniques for IV determination, our aptasensor had a 100-fold lower LOD than immunochromatographic techniques, conceding only to the PCR techniques only, which has the LOD in the range of 102 to 103 virus particles. Two key features allowed achieving the high sensitivity in our assay. The first feature was excitation with the 532 nm laser that corresponds to the shortwave range. The second feature was optimization of the peak of plasmon absorption of SERS substrates so that it is close to excitation wavelength. The optimized SERS substrates were as efficient as metal periodic clusters at 532 nm excitation wavelength but are much more easy and cheap in production.
Further efforts could be implemented to enhance sensitivity. The sensitivity of SERS- based IV detection could be enhanced using nanoparticles instead of a SERS reporter. Proof of the principle was demonstrated for an antibody-based microfluidic sensor with SERS detection, where the LOD was as low as 74 pg/mL, which corresponds to 2.5�102 VP/mL if using 180 MDa as the mass of a virus particle. Although the LOD of our technique was low but not the lowest one; the technique had obvious advantages as it does not requires antibodies, microfluidics, or nanoparticles. The total time for sandwich assay and measurement of a single sample does not exceed 20 minutes. The cost of consumables for the single analysis is low being less than ten dollars.