Optical filtering technologies for integrated fluorescence sensors

Abstract

Numerous approaches have been taken to miniaturizing fluorescence sensing, which is a key capability for micro-total-analysis systems. This critical, comprehensive review focuses on the optical hardware required to attenuate excitation light while transmitting fluorescence. It summarizes, evaluates, and compares the various technologies, including filtering approaches such as interference filters and absorption filters and filterless approaches such as multicolor sensors and light-guiding elements. It presents the physical principles behind the different architectures, the state-of-the-art micro-fluorometers and how they were microfabricated, and their performance metrics. Promising technologies that have not yet been integrated are also described. This information will permit the identification of methods that meet particular design requirements, from both performance and integration perspectives, and the recognition of the remaining technological challenges. Finally, a set of performance metrics are proposed for evaluating and reporting spectral discrimination characteristics of integrated devices in order to promote side-by-side comparisons among diverse technologies and, ultimately, to facilitate optimized designs of micro-fluorometers for specific applications.

Noise analysis and measurement of integrator-based sensor interface circuits for fluorescence detection in lab-on-a-chip applications

“…These filters contain multiple layers of different index materials which cause components of the light to reflect and destructively interfere with the incoming light. By precisely depositing these layers, sharp cut off frequencies can be achieved by such filters [5]. These filters also typically provide incredible high attenuation (OD E < 5).…”

“…In confocal optical systems the LCE is dictated by the Numerical Aperture (NA) of the device optics [18]. In integrated devices, such as the one presented by Burns et al [41] where the detector is placed directly below the microfluidic channel, the LCE of Fluorescence (LCE F l ) is determined by the size of the detector and the distance between the detector and the channel [5]. By modelling the fluorescences as an isotropic source (as shown in Figure 2.3a) it can be shown that the LCE will follow the relationship shown in Eq.…”

“…A review by Dandin et al examined various µTAS FD devices and concluded that, despite many demonstrations of this technology, none has achieved sufficient sensitivity for low-brightness samples [5]. The metric of sensitivity for FD is the limit of detection (LOD) which is the concentration of fluorophore measurable at a given minimum signal-to-noise ratio (SNR).…”

“…The most common signal-acquisition [1,3,5] in conventional biological assays are optical and electrochemical detection. Although the latter has been successfully employed in a number of commercial POC products [6,7], it has found less commercial use in genetic analysis or other low concentration immunoassays due to its limited sensitivity.…”

“…has not yet reached the level of integration and cost suitable for commercial POC devices [5]. Market research has suggested that for LOC devices to be successful in the current marketplace, they need to reach a manufacturing cost of $5 per test [10].…”