Label-free impedance detection of cancer cells from whole blood on an integrated centrifugal microfluidic platform.

An electrochemical Lab-on-a-Disc (eLoaD) platform for the automated quantification of ovarian cancer cells (SKOV3) from whole blood is reported. This centrifugal microfluidic system combines complex sample handling, i.e., blood separation and cancer cell extraction from plasma, with specific capture and sensitive detection using label-free electrochemical impedance. Flow control is facilitated using rotationally actuated valving strategies including siphoning, capillary and centrifugo-pneumatic dissolvable-film (DF) valves. For the detection systems, the thiol-containing amino acid, L-Cysteine, was self-assembled onto smooth gold electrodes and functionalized with anti-EpCAM. By adjusting the concentration of buffer electrolyte, the thickness of the electrical double layer was extended so the interfacial electric field interacts with the bound cells. Significant impedance changes were recorded at 117.2 Hz and 46.5 Hz upon cell capture. Applying AC amplitude of 50 mV at 117.2 Hz and open circuit potential, a minimum of 214 captured cells/mm(2) and 87% capture efficiency could be recorded. The eLoaD platform can perform five different assays in parallel with linear dynamic range between 16,400 and (2.6±0.0003)×10(6) cancer cells/mL of blood, i.e. covering nearly three orders of magnitude. Using the electrode area of 15.3 mm(2) and an SKOV3 cell radius of 5 µm, the lower detection limit is equivalent to a fractional surface coverage of approximately 2%, thus making eLoaD a highly sensitive and efficient prognostic tool that can be developed for clinical settings where ease of handling and minimal sample preparation are paramount.

Label-free impedance detection of cancer cells.

Ovarian cancer cells, SKOV3, have been immobilized onto platinum microelectrodes using anti-EPCAM capture antibodies and detected with high sensitivity using electrochemical impedance. The change in impedance following cell capture is strongly dependent on the supporting electrolyte concentration. By controlling the concentration of Dulbecco's phosphate buffered saline (DPBS) electrolyte, the double layer thickness can be manipulated so that the interfacial electric field interacts with the bound cells, rather than simply decaying across the antibody capture layer. Significantly, the impedance changes markedly upon cell capture over the frequency range from 3 Hz to 90 kHz. For example, using an alternating-current (ac) amplitude of 25 mV, a frequency of 81.3 kHz, and an open circuit potential (OCP) as the direct-current (dc) voltage, a detection limit of 4 captured cells was achieved. Assuming an average cell radius of 5 µm, the linear dynamic range is from 4 captured cells to 650 ± 2 captured cells, which is approximately equivalent to fractional coverages from 0.1% to 29%. An equivalent circuit that models the impedance response of the cell capture is discussed.

High sensitivity carbon nanotube based electrochemiluminescence sensor array.

Ink jet printed carbon nanotube forest arrays capable of detecting picomolar concentrations of immunoglobulin G (IgG) using electrochemiluminescence (ECL) are described. Patterned arrays of vertically aligned single walled carbon nanotube (SWCNT) forests were printed on indium tin oxide (ITO) electrodes. Capture anti-IgG antibodies were then coupled through peptide bond formation to acidic functional groups on the vertical nanotubes. IgG immunoassays were performed using silica nano particles (Si NP) functionalized with the ECL luminophore [Ru(bpy)(2)PICH(2)](2+)], and IgG labelled G1.5 acid terminated PAMAM dendrimers. PAMAM is poly(amido amine), bpy is 2,2'-bipyridyl and PICH(2) is (2-(4-carboxyphenyl)imidazo[4,5-f][1,10]phenanthroline). The carboxyl terminal of [Ru(bpy)(2)PICH(2)](2+) (fluorescence lifetime ≈ 682±5 ns) dye was covalently coupled to amine groups on the 800 nm diameter silica spheres in order to produce significant ECL enhancement in the presence of sodium oxalate as co-reactant in PBS at pH 7.2). Significantly, this SWCNT-based sensor array shows a wide linear dynamic range for IgG coated spheres (10(6) to 10(12) spheres) corresponding to IgG concentrations between 20 pM and 300 nM. A detection limit of 1.1±0.1 pM IgG is obtained under optimal conditions.

Ruthenium aminophenanthroline metallopolymer films electropolymerized from an ionic liquid: deposition and electrochemical and photonic properties.

The oxidative electropolymerization of [Ru(aphen)3](PF6)2 from an ionic liquid, 1-butyl-2,3-dimethylimidazolium bis[(trifluoromethyl)sulfonyl]imide (BDMITFSI), is reported; aphen is 5-amino-1,10-phenanthroline. The deposition rate in the ionic liquid is more than an order of magnitude faster than in conventional solvents such as anhydrous acetonitrile and aqueous sulfuric acid. The UV-vis absorbance, Raman, and emission spectra of the films grown in ionic liquid, acetonitrile, and sulfuric acid suggest that the polymer formed does not depend on the solvent. However, scanning electron microscopy shows that the film morphologies differ significantly; e.g., films deposited from BDMITFSI have high surface roughness, while films produced in acetonitrile and sulfuric acid are relatively smooth. The rate of homogeneous charge transport through films grown in ionic liquids is (6.4 +/- 1.2) x 10(-9) cm (2) s (-1), which is approximately 2 orders of magnitude faster than that found for films deposited from acetonitrile. Thin electropolymerized films generate electrochemiluminescence (ECL) in the presence of tripropylamine as a coreactant. Films produced from sulfuric acid are very thin compared to the ones produced in BDMITFSI; however, they produce an ECL signal of similar intensity. The ECL responses of films produced in anhydrous acetonitrile are significantly less intense. The ECL intensity within the films is approximately 5-fold higher than when they are dissolved and measured in solution.