||An amplitude-sensitive paired surface plasma waves biosensor (PSPWB), which is based on SPR in conjunction with an optical heterodyne technique, has been demonstrated to show a detection limit of Δneff = 8.4×10-9 RIU. In addition, the biosensor is capable of real-time detection of total prostate-specific antigen (t-PSA) in phosphate buffered saline (PBS) solution and in diluted human serum without labeling. These experimental results exhibited a linear relationship between surface plasmon resonance (SPR) signals and t-PSA concentrations over a wide range from 10 fg/mL (~300 aM) to 100 pg/mL (~3 pM) and it is without complicated operating procedures when detecting biological analytes in clinical sample. And then, we applied the developed PSPWB in a dual-channel biosensor for rapid and sensitive detection of swine-origin influenza A (H1N1) virus (S-OIV). In conjunction with the amplitude ratio method with a reference channel, the stability of PSPWB system is significantly improved experimentally such that the theoretical LOD of the dual-channel PSPWB for S-OIV is 30 PFU/mL, which was two orders of magnitude more sensitive than the commercial rapid influenza diagnostic test (RIDT) at worst. Furthermore, under in vivo condition, this experiment demonstrates that the assay successfully measured S-OIV at a concentration of 1.8×102 PFU/mL in mimic solution, which contained PBS-diluted normal human nasal mucosa. Most importantly, the assay time took less than 20 min as opposed to several hours by polymerase chain reaction (PCR)-based methods.|
Finally, we establish a method that can calculate the binding constants of protein-protein interactions at ultra-low concentrations based on gold nanoparticle enhancement in sandwich configuration. The association rate constant, dissociation rate constant, equilibrium association constant, and the equilibrium dissociation constant, i.e., ka, kd, KA, KD, respectively, of the kinetics of binding between t-PSA and anti-t-PSA at concentrations from 0.1 pg/mL to 1 ng/mL, were measured either in PBS or in human serum. This is the first time that the kinetic constants have been measured at such a low concentration range in a complex sample such as human serum.
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