Sensitive detection of a tumor marker, α-fetoprotein, with a sandwich assay on a plasmonic chip.

Two types of plasmonic silver- and gold-coated grating biosensor chips (plasmonic chip) were applied in the detection of α-fetoprotein (AFP) with a sandwich imunoassay and surface plasmon field-enhanced fluorescence. On the plasmonic chip, unlabeled marker in the sandwich immunoassay was first quantitatively detected over a wide range between 10(-12) and 10(-8) g/mL. The affinity constants between AFP and anti-AFP antibody, which were obtained by fitting the experimental data to the Langmuir isotherm adsorption curve, were 1 × 10(8) g(-1) mL regardless of the kind of metal in the plasmonic chips. Although the fluorescence intensity on the silver plasmonic chip was 5 times larger than that on the gold plasmonic chip, the limit of detection (LOD) was on the order of 10(-11) g/mL and not improved with a silver plasmonic chip. Herein, we used a new setup that generated less dispersions of both the fluorescence intensity for nonspecific adsorption and the background (optical blank) signal and improved the LOD of AFP to 4 pg/mL (55 fM) with the silver plasmonic chip. With the highly sensitive detection in the sandwich immunoassay, the development of a plasmonic chip for clinical diagnosis by a blood test is promising.

Correlation between human health and reactive oxygen species produced in blood: a long-term chemiluminescence and fluorescence analysis.

The previous slide-glass type system could simultaneously detect reactive and highly reactive oxygen species, i.e., superoxide radicals (O2-·) and hypochlorite ions (OCl-) elicited from leucocytes in sample blood, but had some drawbacks, i.e., signal noise from air-flow stirring, potential biohazard risks, etc. because of open samples placed on a slide glass. We overcame these drawbacks by adopting a fluidic-chip container in a new system, which resulted in higher sensitivity and more stable measurements. Using the new system, we conducted a pilot study on nominally healthy volunteers to find whether or not the monitored activities of leukocytes can distinguish more or less unhealthy conditions from healthy ones. At first, healthy volunteers of both genders and of various ages showed that the fluctuation magnitudes (%) of O2-· and OCl- were nearly similar to each other and to that of the neutrophil count fluctuation. These parameters sometimes exceeded the healthy fluctuation range. By comparing these large fluctuations with the data of an inflammation marker C-reactive protein (CRP), the neutrophil count fluctuation and the timings/symptoms of abnormalities found in questionnaire, we could gain information suggesting the factors causing the large fluctuations. The new system could detect bodily abnormalities earlier than CRP or self-aware symptoms.