Electrochemical study of ricin at glassy carbon electrode.

Ricin, Ricinus communis agglutinin 60 - RCA 60, is a deadly phytotoxic protein which inhibits ribosomes (class II), and there is no known effective antidote in living organisms. Ricin is composed of two polypeptide chains, A and B, linked covalently by a single disulfide bond. The analytical methods for the detection of RCA 60 are commonly laborious, expensive, require skilled labor, and involve sophisticated equipment. Aimed at the development of electroanalytical methods for RCA 60 detection, here we studied the electrochemical oxidation of RCA 60 on a glassy carbon (GC) electrode over a wide pH range, using cyclic voltammetry, differential pulse voltammetry (DPV) and square wave voltammetry (SWV). Two quasi-reversible electrochemical RCA 60 oxidation peaks were identified on the GC electrode by SWV. For values of 2.2 ≤ pH ≤ 10.2, DPV studies revealed that the peak potentials, EP1 and EP2, display a linear dependence with pH and the reaction mechanism involves the transfer of 2H⁺/2e⁻ (peak 1) and 1H⁺/1e⁻ (peak 2). The first and second RCA 60 oxidation steps may correspond to the oxidation of cysteine and tyrosine-tryptophan residues, respectively. The oxidation product of the second RCA 60 oxidation step appears at 7.0 ≤ pH ≤ 11.8. For pH ≥ 10.2, both processes are pH independent, resulting in a pKa of ca. 10.2. A third RCA 60 oxidation peak only appears at acidic pH. RCA 60 samples extracted from different castor seed cultivars showed similar electrochemical behavior, enabling the implementation of an analytical voltammetric method.

Three-dimensional large-scale microfluidic integration by laser ablation of interlayer connections.

Multilayer Soft Lithography (MSL) is a robust and mature fabrication technique for the rapid prototyping of microfluidic circuits having thousands of integrated valves. Despite the success and wide application of this method, it is fundamentally a planar fabrication technique which imposes serious design constraints on channel routing, feature density, and fluid handling complexity. We present here methods and related instrumentation to remove these limitations by combining the advantages of MSL processing with laser micromachining using a CO(2) laser ablation system. This system is applied to both the dense integration of layer-layer interconnects and the direct writing of microchannels. Real-time image recognition and computer control allow for robust wafer-scale registration of laser ablation features with moulded channel structures. Ablation rates of up to 8 Hz are achieved with positional accuracy of approximately 20 microm independent of mechanical distortions in the elastomer substrate. We demonstrate these capabilities in the design and fabrication of a production scale multi-laminate micromixer that achieves sub-millisecond mixing of two streams at flow rates up to 1 mL min(-1). The marriage of laser micromachining with MSL-based valve integration allows for high-yield fabrication of topologically complex microfluidic circuits having thousands of layer-layer interconnects and integrated valves.