Fluorescence Multi-Detection Device Using a Lensless Matrix Addressable microLED Array

Abstract

A Point-of-Care system for molecular diagnosis (PoC-MD) is described, combining GaN and CMOS chips. The device is a micro-system for fluorescence measurements, capable of analyzing both intensity and lifetime. It consists of a hybrid micro-structure based on a 32 × 32 matrix addressable GaN microLED array, with square LEDs of 50 µm edge length and 100 µm pitch, with an underneath wire bonded custom chip integrating their drivers and placed face-to-face to an array of 16 × 16 single-photon avalanche diodes (SPADs) CMOS. This approach replaces instrumentation based on lasers, bulky optical components, and discrete electronics with a full hybrid micro-system, enabling measurements on 32 × 32 spots. The reported system is suitable for long lifetime (>10 ns) fluorophores with a limit of detection ~1/4 µM. Proof-of-concept measurements of streptavidin conjugate Qdot™ 605 and Amino PEG Qdot™ 705 are demonstrated, along with the device ability to detect both fluorophores in the same measurement.

Keywords: CMOS; GaN; Point-of-Care; SPAD; fluorescence; lifetime fluorescence; microLED array; microLED driver; multiplex.

Figure 1

The schematic view of the setup is shown in (a), and a picture of the setup is in (b). (c) is a microscopic picture of the array of microLEDs with different LEDs turned on and (d) is a picture of the CMOS driver wire bonded to the PCB.

Figure 2

Image of the LED chip with the anodes at the right side and the cathodes at the top. As can be observed in the image, only 32 anode connections and 32 cathode connections are needed for an array of 32 × 32 LEDs [51].

Figure 3

Short pulse generation circuit (a) and the anode and cathode driving elements (b). The anode and cathode driving circuits are composed of high voltage output buffers (M7–M8 for the anode driver and M9–M10 for the cathode driver) and level shifters (M5–M6 and M11–M12) with a NAND gate per driver to select the specific LED.

Figure 4

Driving circuit turning off a microLED for different bias voltages. It can be observed that the turn off time is the same for all the bias voltage, therefore making the circuit speed robust to changes in the driving voltage of the LEDs. The y axis (Counts) represents the optical intensity captured by the SPAD sensor.

Figure 5

LEDs at 6V bias voltage (a) without any calibration. Each LED emits different power. In (b) all the LEDs were calibrated to 150 kcounts. In (b) there are visible non-working LEDs.

Figure 6

Image acquired by the device, where QD605 is detected in the orange areas (above 1000 counts in each one). The other part of the image corresponds to absence of QD605.

Figure 7

Intensity obtained in different measurements for different concentrations of QD605 and QD705.

Figure 8

Decay time for QD605 at a concentration of 1 µM (a) (with A = 1953 and τ = 32.1 ns) and for QD705 also at a concentration of 1 µM (b) (with A = 306 and τ = 80.4 ns). In both cases, it is shown the fitted line (in red) where the amplitudes (A) and the lifetimes (τ) are obtained. (c,d) correspond to a mixture of QD605/QD705 in ratio 1 µM/1 µM and 0.5 µM/1 µM, respectively. Bi-exponential fitting results in A₁ = 1915 and τ₁ = 32.1 ns; A₂ = 417 and τ₂ = 81.1 ns in (c) and A₁ = 989 and τ₁ = 32.2 ns; A₂ = 397 and τ₂ = 80.9 ns in (d).

Figure 9

Lifetimes of QD605 (blue) and QD705 (green) for 1 µM for 100 sampled measurements to extract statistical values.

Figure 10

Image obtained with the device where the two fluorophores were deposited in microwells.