Proceedings Article | 11 April 2007
KEYWORDS: Silicon, Adsorption, Gold, Proteins, Atomic force microscopy, Blood, Sensors, Molecules, Sodium, Statistical analysis
Patients with renal failure become not able to expel the waste product, and they accumulate the toxic products for
themselves. They therefore must use the hemodialysis to weed out the metabolic decomposition product. Hemodialysis
for chronic renal failure is the most popular treatment method with artificial organs. However, hemodialysis patients
must continue the treatment throughout their life, the results of long term extracorporeal dialysis, those patients develop
the various complications and diseases, for example, dialysis amyloidosis etc. Dialysis amyloidosis is one of the
refractory complications, and the prevention of this complication is important. Recently, endotoxin is thought to be the
most likely cause of the complication.
Endotoxin is one of the major cell wall components of gram-negative bacteria, and it forms the complex with proteins
and lipopolysaccharide (LPS). It has various biological activities, e.g. attack of fever, when it gets mixed into human
blood. In addition, it is known that large amount of endotoxin exists in living environment, and medicine is often
contaminated with endotoxin. When contaminated dialyzing fluids are used to hemodialysis, above-mentioned dialysis
amyloidosis is developed. Therefore, it is important that the detection and removal of endotoxin from dialyzing fluids.
Until now, the measurement methods using Limulus Amebosyte Lysate (LAL) reagent were carried out as the tests for
the presence of endotoxin. However, these methods include several different varieties of measurement techniques. The
following are examples of them, gelatinization method, turbidimetric assay method, colorimetric assay method and
fluoroscopic method. However, these techniques needed 30-60 minutes for the measurement. From these facts, they are
not able to use as a "real-time endotoxin detector". The detection of endotoxin has needed to carry out immediately, for
that reason, a new "real-time" detection method is desired.
We focused attention to adsorption reaction between &egr;-polylysine and endotoxin. &egr;-polylysine has the structure of
straight chain molecule composed by 25-30 residues made by lysine, and it is used as an antimicrobial agent, moreover,
cellulose beads with immobilized &egr;-polylysine is used as the barrier filter for endotoxin removal. Therefore, it is
expected that the endotoxin be adsorbed to the immobilized &egr;-polylysine onto the probe. As the result of this reaction,
the mass of the probe is increased, and endotoxin can be detected by using of Quartz Crystal Microbalance (QCM). In
our previous research, we have already acquired the proteins immobilization technique onto Au and Si surface. In this
report, the proposal of molecular adsorption type endotoxin detection system, and the immobilization of &egr;-polylysine
onto the probe are described. We use X-ray Photoelectron Spectroscopy (XPS) to confirm the &egr;-polylysine
immobilization, and the adsorptive activity of immobilized &egr;-polylysine is measured by XPS and AFM. The purpose of
this study is to bring about the realization of "Real-time endotoxin detection system".
