Handheld instruments


Figure 2. A typical PoC diagnostic fluorescence detection system


By Wassim Bassalee, field applications engineer, Aileen Cleary, marketing manager, Medical Instrumentation and Life Sciences Business Group, Rob Finnerty, systems applications engineer, and Neil Quinn, systems applications engineer, Analog Devices


and consequently achieve better sensitivity without sacrificing selectivity, a careful design of the optical detection system is needed to ensure that the electronic receive chain does not contribute to the background noise level.


A TYPICAL POC FLUORESCENCE DETECTION SYSTEM A typical PoC diagnostic fluorescence detection system employs a light emitting diode (LED) to generate the excitation light and employs a photodiode (PD) to detect the fluorescence emission from the sample. The PD generates an electrical current that is proportional to the intensity of the fluorescence signal, which can be extremely weak. The PD current is often very small relative to the noise floor, necessitating careful electronic design for achieving high sensitivity detection without sacrificing selectivity. Figure 2 shows the main elements of a typical PoC fluorescence detection system. The current


signal from the PD is converted to a voltage signal by the trans-impedance amplifier (TIA). The voltage signal is digitised by the analogue- to-digital converter (ADC) and translated into a corresponding level of fluorescence.


THE PERFORMANCE NEEDS OF A FLUORESCENCE DETECTION POC SYSTEM Designers of PoC systems strive to achieve maximum diagnostic sensitivity without sacrificing selectivity. In regard to PoC instruments, this goal translates into the requirement of reliably discerning very low PD current in response to LED excitation. For example, a high sensitivity system must be able to detect PD currents on the order of picoamperes in response to LED excitation currents on the order of 100 mA. That is, the system must be able to detect PD fluorescence given approximately 140 dB of optical attenuation.


Figure 3. A PoC detection system using an integrated optical front end. Instrumentation Monthly May 2023


Continued on page 56... 55


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82