Dual-point dual-wavelength fluorescence monitoring of DNA separation in a lab on a chip

Microfluidic-controlled optical router for lab on a chip

In multiplexed analysis, lab on a chip (LoC) devices are advantageous due to the low sample and reagent volumes required. Although optical detection is preferred for providing high sensitivity in a contactless configuration, multiplexed optical LoCs are limited by the technological complexity for integrating multiple light sources and detectors in a single device. To address this issue, we present a microfluidic-controlled optical router that enables measurement in four individual optical channels using a single light source and detector, and without movable parts. The optofluidic device is entirely fabricated in polydimethylsiloxane (PDMS) by soft-lithography, compatible with standard microfabrication technologies, enabling monolithic integration in LoCs. In the device, in-coupled light from an optical fiber is collimated by a polymeric micro-lens and guided through a set of four sequentially connected micro-chambers. When a micro-chamber is filled with water, light is transmitted to the next one. If it is empty of liquid, however, total internal reflection (TIR) occurs at the PDMS-air interface, re-directing the light to the output optical fiber. The router presents high performance, with low cross-talk (<2%) and high switching frequencies (up to 0.343 ± 0.006 Hz), and provides a stable signal for up to 91% of the switching time. With this miniaturized, low-cost, simple and robust design, we expect the current technology to be integrated in the new generation of multiplexed photonic LoCs for biomarker analysis, even at the point of care.

Development of dual-color total internal reflection fluorescence biosensor for simultaneous quantitation of two small molecules and their affinity constants with antibodies

A novel dual-color total internal reflection fluorescence biosensor (DTB) was successfully developed for the simultaneous detection of two small molecules based on a simple optical structure and the time resolved effect of fiber optic switch. The DTB employed a single-multi mode fiber optic coupler instead of a sophisticated confocal optical system for the transmission of two excitation lights and dual-color fluorescence, and a photodiode detector instead of photomultiplier for the simultaneous detection of dual-color fluorescence. The compact optical design of DTB improved its optical transmission efficiency and detection sensitivity because of no requirement of numerous optical separation elements and rigorous optical alignment. The DTB was applied for the simultaneous detection of 2,4-Bisphenol-A (BPA) and 2,4-Dichlorophenoxyacetic acid (2,4-D) using one bifunctional fiber optic bio-probe modified by two hapten-protein conjugates. When the mixture of Cy5.5 labeled anti-2,4-D antibody and Pacific Blue dye labeled anti-BPA antibody was introduced over the surface of the bio-probe, they bound with their respective hapten-protein conjugate immobilized onto the bio-probe. Based on the time-resolved effect of fiber optic switch, two fluorescence dyes were alternatively excited by 635 nm and 405 nm laser lights and simultaneously detected by one photodiode detector. Taking indirect competitive immunoassay principle, BPA and 2,4-D were simultaneously detected using the DTB with high sensitivity, accuracy, and rapidity. The quantitation of affinity constants between small molecules and their antibodies was also achieved based on the proposed theory. The DTB provides a flexible and powerful platform for simultaneously sensitive quantitation of multiple targets and the affinity constants of biomolecular interactions.

A Perspective on the Rise of Optofluidics and the Future

In the recent past, the field of optofluidics has thrived from the immense efforts of researchers from diverse communities. The concept of optofluidics combines optics and microfluidics to exploit novel properties and functionalities. In the very beginning, the unique properties of liquid, such as mobility, fungibility and deformability, initiated the motivation to develop optical elements or functions using fluid interfaces. Later on, the advancements of microelectromechanical system (MEMS) and microfluidic technologies enabled the realization of optofluidic components through the precise manipulation of fluids at microscale thus making it possible to streamline complex fabrication processes. The optofluidic system aims to fully integrate optical functions on a single chip instead of using external bulky optics, which can consequently lower the cost of system, downsize the system and make it promising for point-of-care diagnosis. This perspective gives an overview of the recent developments in the field of optofluidics. Firstly, the fundamental optofluidic components will be discussed and are categorized according to their basic working mechanisms, followed by the discussions on the functional instrumentations of the optofluidic components, as well as the current commercialization aspects of optofluidics. The paper concludes with the critical challenges that might hamper the transformation of optofluidic technologies from lab-based procedures to practical usages and commercialization.

Frequency-encoded laser-induced fluorescence for multiplexed detection in infrared-mediated quantitative PCR

A frequency-modulated fluorescence encoding method was used as a means to increase the number of fluorophores monitored during infrared-mediated polymerase chain reaction. Laser lines at 488 nm and 561 nm were modulated at 73 and 137 Hz, respectively, exciting fluorescence from the dsDNA intercalating dye, EvaGreen, and the temperature insensitive dye, ROX. Emission was collected in a color-blind manner using a single photomultiplier tube for detection and demodulated by frequency analysis. The resulting frequency domain signal resolved the contribution from the two fluorophores as well as the background from the IR lamp. The detection method was successfully used to measure amplification of DNA samples containing 10(4)-10(7) starting copies of template producing an amplification efficiency of 96%. The utility of this methodology was further demonstrated by simultaneous amplification of two genes from human genomic DNA using different color TaqMan probes. This method of multiplexing fluorescence detection with IR-qPCR is ideally suited as it allows isolation of the signals of interest from the background in the frequency domain and is expected to further reduce the complexity of multiplexed microfluidic IR-qPCR instrumentation.

Optofluidic approaches for enhanced microsensor performances

Optofluidics is a relatively young research field able to create a tight synergy between optics and micro/nano-fluidics. The high level of integration between fluidic and optical elements achievable by means of optofluidic approaches makes it possible to realize an innovative class of sensors, which have been demonstrated to have an improved sensitivity, adaptability and compactness. Many developments in this field have been made in the last years thanks to the availability of a new class of low cost materials and new technologies. This review describes the Italian state of art on optofluidic devices for sensing applications and offers a perspective for further future advances. We introduce the optofluidic concept and describe the advantages of merging photonic and fluidic elements, focusing on sensor developments for both environmental and biomedical monitoring.

A hybrid silicon-PDMS optofluidic platform for sensing applications

A hybrid silicon-poly(dimethysiloxane) (PDMS) optofluidic platform for lab-on-a-chip applications is proposed. A liquid-core waveguide with a self-aligned solid-core waveguide and a microfluidic device are integrated with a multilayer approach, resulting in a three-dimensional device assembly. The optofluidic layer was fabricated with a hybrid silicon-polymer technology, whereas the microfluidic layer was fabricated with a soft lithography technique. The combination of different materials and fabrication processes allows a modular approach, enabling both the benefits from the high optical quality achievable with silicon technology and the low cost of polymer processing. The proposed chip has been tested for fluorescence measurements on Cy5 water solutions, demonstrating the possibility to obtain a limit of detection of 2.5 nM.

Modulation-frequency encoded multi-color fluorescent DNA analysis in an optofluidic chip

We introduce a principle of parallel optical processing to an optofluidic lab-on-a-chip. During electrophoretic separation, the ultra-low limit of detection achieved with our set-up allows us to record fluorescence from covalently end-labeled DNA molecules. Different sets of exclusively color-labeled DNA fragments-otherwise rendered indistinguishable by spatio-temporal coincidence-are traced back to their origin by modulation-frequency-encoded multi-wavelength laser excitation, fluorescence detection with a single ultrasensitive, albeit color-blind photomultiplier, and Fourier analysis decoding. As a proof of principle, fragments obtained by multiplex ligation-dependent probe amplification from independent human genomic segments, associated with genetic predispositions to breast cancer and anemia, are simultaneously analyzed.