Ultra-small Sample Research Articles

SPCE Based Glucose Sensor Employing Novel Thermostable Glucose Dehydrogenase, FADGDH: Blood Glucose Measurement with 150nL Sample in One Second

Self-monitoring of blood glucose (SMBG) is an important component of the modern therapy for diabetes mellitus. Thanks to the current progress in electronics and sensor fabrication technology, both the time and the blood sample volume required for the measurement have decreased drastically. However, devices that work with an even smaller sample volume and a shorter measurement time are in demand. A disposable glucose sensor that works with an ultra-small sample volume was developed employing the novel thermostable glucose-dehydrogenase (FADGDH) complex composed of a catalytic subunit, an electron transfer subunit (cytochrome c), and a small subunit. The electrode is a screen-printed carbon electrode (SPCE), and hexaammineruthenium (III) chloride (Ru complex) is utilized as the electron mediator. A disposable enzyme sensor was constructed by depositing the FADGDH complex and Ru complex onto the SPCE, and the sensor performance was evaluated. Whole-blood glucose can be measured within 1 sec using this enzyme sensor and a 150-nL whole-blood sample, with high precision (>0.99br>) and high reproducibility (CV<0.45%br>) within the glucose concentration range of 0-533 mg/dL. The sensor reading was stable for more than 60 days even at 70 degrees C. The simplicity of the construction and the high precision of this FADGDH-based glucose biosensor makes it an alternative to previously reported commercially available glucose sensors. Especially the sample volume of 150 nL and the 1-sec measurement time are the highest specifications in the world for currently available glucose sensors designed for the SMBG.

Selective detection of antibodies in microstructured polymer optical fibers

We demonstrate selective detection of fluorophore labeled antibodies from minute samples probed by a sensor layer of complementary biomolecules immobilized inside the air holes of microstructured Polymer Optical Fiber (mPOF). The fiber core is defined by a ring of 6 air holes and a simple procedure was applied to selectively capture either alpha-streptavidin or alpha-CRP antibodies inside these air holes. A sensitive and easy-to-use fluorescence method was used for the optical detection. Our results show that mPOF based biosensors can provide reliable and selective antibody detection in ultra small sample volumes.

Injection of ultrasmall samples and single molecules into tapered capillaries.

A novel injection scheme is described in which ultrasmall samples in the attoliter (10(-18) L) and low femtoliter (10(-15) L) range, or even single molecules, are controllably introduced into a tapered capillary so that electrophoretic separation can be carried out. To match the dimensions of the capillary inlet with that of the sample, capillary tips are tapered to an inside diameter ranging from hundreds of nanometers to a few micrometers. To inject an ultrasmall sample, optical trapping is used to immobilize and manipulate the sample in order to place it inside or next to the capillary inlet. A small controlled suction results in the loading of the sample into the capillary.

Quantitative determination of transferrin in cerebrospinal fluid using an enzyme linked immunosorbent assay.

An enzyme linked immunosorbent assay (ELISA) based method for the determination of transferrin in cerebrospinal fluid (CSF) is described. This method allows transferrin determinations in ultra-small (</= 5 microL) sample volumes. The proposed method offers the possibility to determine transferrin at very low concentrations at which existing methodologies fail because of their insufficient detection limits. The accuracy of the proposed technique was validated by comparing the results of 20 CSF samples obtained by ELISA to those measured by nephelometry yielding mean +/- SD values of 21.1+/-5 mg/L and 20.6 +/- 6 mg/L, respectively (y = 1.13X - 2.97, r = 0.899). The interassay CV was below 10% whereas the detection limit was 2.9 microg/L.