A modular microfluidic architecture for integrated biochemical analysis

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   Fig. 1.

   Microfluidic breadboard system-level architecture. (A) Schematic diagram of a representative FBB consisting of electromechanical components and through-wafer fluidic connections. (B) A complete LOC can be built by bonding a passive fluidic chip with an FBB. (Inset) A perspective view emphasizing the fluidic communication between components on two levels. (C) Different functions may be realized by deploying different passive chips on the same FBB. (D) Multiple chips can be interconnected to form a larger system at the multiple-chip module level.

   
   
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   Fig. 2.

   First-generation FBB implementation. (A) The system was assembled by reversibly bonding a passive PDMS chip to the FBB, which consisted of an active PDMS chip bonded to an oxidized silicon wafer with through-wafer holes. (B) Pneumatically actuated valves were formed at the crossing of the pneumatic control (red) and fluid (blue) channels on the active chip. Single valves may be used to control sample loading, whereas multiple valves can be used for multipath switching. (C) An optical micrograph of a single LOC. Holes were punched in the PDMS chip to provide pneumatic connection ports to the valve control channels. (D1) Cross-sectional view of the LOC emphasizing the operation of a single valve. (D2) An empty channel is cut off by a thin PDMS membrane actuated via pneumatic pressure. (D3) Fluid may be filled up to the closed valve as air escapes through the PDMS. (D4) Releasing the pressure in the pneumatic control line opens the valve and allows the fluid to continue flowing.

   
   
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   Fig. 3.

   Subsystem for mixing picoliter-scale volumes of fluid. Video frames illustrate the process by which precise volumes of fluid are loaded into either side of a microreactor and then mixed by diffusion. A concentrated solution of Cresol red (a pH indicator) in 0.1 M sodium hydroxide (NaOH) titrated with hydrochloric acid is loaded into the right half of the reactor (400 pl), stopped by a valve oriented along the length of the chamber. An equal volume of 0.1 M NaOH is loaded into the left half at the same time. The reactor is then isolated and the valve separating the fluids is opened to allow mixing, indicated by a color change from yellow to purple. Finally, the mixture is purged from the chamber and transferred to the passive chip on the opposite side of the FBB (not visible).

   
   
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   Fig. 4.

   System design for the detection of fPSA with the BBC protocol. The PSA is sandwich-captured and separated in the first stage of the device (because of an applied magnetic field) by flowing solutions from the inlet to the waste outlet with valve 2 closed and valve 1 open. Indirect amplification is provided by bar-code DNA that is released from the sandwich and transferred from the FBB to the detection chip. Valve 1 and valve 3 are closed, whereas valve 2 is opened to allow the bar-code transfer. The bar codes attach to the surface of the DNA-modified detection chip and are sandwiched with gold NPs that are then silver-stained to provide a direct optical readout of the result.

   
   
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   Fig. 5.

   Fabricated device and testing results for the detection of fPSA. (A) The system is capable of concurrently performing eight different BBC tests by connecting four identical chips to a centralized detection chip. (B) Each chip can run two simultaneous tests. (C) fPSA was detected at concentrations ranging from 50 fM to 500 aM based on the intensity of scattered light off the silver-stained NPs.

   
   
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   Fig. 6.

   Low-level Pb²⁺ (lead) detection with a DNAzyme-based fluorescent biosensor. (A) The DNAzyme biosensor is made of a cleavable substrate annealed with an enzyme strand. A fluorescent probe (FAM) located on the 5′ end of the substrate is quenched by probes (Dabcyl) on both strands until the presence of lead causes the enzyme strand to cleave the substrate, resulting in increased fluorescence. (B) The biosensor was mixed with samples containing lead by using the picoliter-scale reactor on the FBB. Four samples were processed simultaneously in four separate reactors. (C) The samples were then transferred to the detection area on the passive chip. (D) Lead was detected from 10 μM to 500 nM by measuring the fluorescence intensity of the four results.