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70 PCB007 MAGAZINE I APRIL 2020 natural partner for LoC development and the scope to be straightforwardly up-scaled. Enter Dr. Despina Moschou, a researcher at the Centre for Advanced Sensor Technologies, Department of Electronic and Electrical Engi- neering at the University of Bath in the U.K. Dr. Moschou is a frequent speaker at printed circuit events like AltiumLive [1], EIPC Confer- ences, and the ICT Conferences. Fortunately, for us, she has taken the time to prepare sum- maries of her, and the many others in this field, work on LoC and LoPCB µTAS approaches. Early experimentation was focused on bio- electrodes for PCBs and on the microfluid- ics compatible with PCB fabrication. Figure 8 shows a test vehicle. This was a two-sided FR- 4 PCB with gold plated copper traces and sen- sor electrodes. Two different gold were tested. One was a soft gold—the Metalor R MetGold Pure ATF process, plated 2.57 µm layer of 90 HV hardness. For the hard gold, the Metalor R EnGold 2015CVR process was followed, pro- viding 2.41 µm of gold on top of 3.41 µm of nickel with a final hardness of 140–180 HV. To handle the delicate microfluidics, the properties of dry film photoresist (like DuPont RistonTM, or DFR) was employed. This photo- sensitve material, with proper cur- ing, can be stabilized for long life, and—in some applications—can be used as a photosensitive adhesive. Too bad that the dry-film solder mask (DFSM), like DuPont VacrelTM, was no longer available. A thin FR-4 lay- er (200 µm) was laminated with a 50 µm DFR, that was patterned us- ing standard PCB photolithography, developed and cured for two hours to drive off any solvents. Then, ad- hesive-based flexible cover coating of PMMA film was laser microma- chined to provide for larger fluidic supply channels (~5 mm), and the stackup laminated to the FR-4 sens- ing layer. Dr. Moschou's recent work is shown in Figure 9, which is a three- layer multilayer experiment where the construction is: • Layer 1: Reference layer plated with copper, silver, and silver chloride (Figure 5b&c) • Layer 2: Sensing electrodes plated with hard gold • Layer 3: the microfluidic layers for the sample solution A 3D exploded view, as well as the plated layers, are also shown. The experimental test board proved very successful, so a full LoPCB substrate was designed (Figure 10). This fully integrated PCB cartridge (4.6 cm x 5.7 cm) in- cludes the microfluidic channels for handling the sample, reference electrodes, and working electrodes. It is designed to measure the bio- markers for the test for tuberculosis. In addi- tion to the three-layer construction, the car- tridge contained: • PCI express electrical interfacing • Six channels (four standard curve points within the clinical range, one negative control, and one sample) • 10 µL reaction chambers • Three amperometric sensors per channel • Full assay implemented on the PCB Figure 7: LoC sequence using glass microchannels for micro LC/MS of medical samples [2] .