In this class of sensors, point of care testing (POCT) is playing a revolution in the approach of sensing analytes of clinical interest . Up to the Nineties, any type of clinical analysis was performed in central laboratories which were equipped by expensive, sophisticated but heavy and not portable instrumentation.
The progress in electronics combined with the advent of micro and nanotechnologies has allowed the reduction in the instrumentation size, giving the possibility to move the instrumentation from the central laboratory to the patient’s bed and leading the advent of point of care testing, i.e. medical testing at or near the site of patient care. This transformation meets the wishes of physicians who are asking for medical devices capable to provide a fast and reliable measurement of clinical parameters in order to formulate the right diagnosis or to decide the correct therapy in a short time.
In this view optical biochips can play a fundamental role. A biochip can be considered an array of individual biosensors that can be individually monitored and generally are used for the analysis of multiple analytes.
Two main classes can be distinguished label-free devices, in which the interaction analyte/sensitive layer gives rise to a modification of the optical signal due to the change of the refractive index of the layer deposited on the substrate. Label-based devices are those in which luminescent labeling is used to get an optical signal depending on the investigated analyte. Both approaches have advantages and disadvantages.
Label-free sensors have the advantage of analysis without the label application. This aspect should not be underestimated as the chemical modification to which the biological recognition elements are subjected due to the chemical attachment of the luminescent label, implies a more or less pronounced modification in their affinity to the investigated analyte. This can lead to cross sensitivity to non-target compounds. However, for monitoring complex samples, the label-free methods can be more susceptible to problems such as low sensitivity and increased backgrounds due to non-specific binding. In contrast to genomics and proteomics, in which thousands of sensing spots are monitored simultaneously by means of fluorescence scanners, many POCT applications often require the measurement of only a limited number of parameters to identify the correct pathology or to monitor the administrated therapy.
Some portable instrumentations are already available on the market such as the devices from Roche (Cardiac Reader and TROP T) or from Biosite (Triage Meters) for the measurement of cardiac markers (troponin, myoglobin, Ddimer, brain-type natriuretic peptide, creatine kinase-MB) in 15–20 min. It is apparent that, in the case of possible infarction, saving time, also a few minutes, in making the correct diagnosis can be crucial for the patient’s survival. But the timeliness in a correct diagnosis can be also essential in many other cases, such as the discrimination of viral and bacterial sepsis in intensive care patients or the fast identification of the origin of infections. In this case, the simultaneous measurements of analytes such as creactive protein, procalcitonin, tumour necrosis factor Į, interleukine-6, interleukine-8, interleukine-10 and neopterin can be extremely important for physicians.
Extracted and edited from “The optical solution in biosensing by F. Baldini“