**5.4 Reflectometric interference spectroscopy (RIfS)**

In order to investigate molecular interaction, a physical technique known as reflectometric interference spectroscopy is used. This technique depends on white light being interfered at thin films as shown in **Figure 6**. In Reflectometric Interference Spectroscopy (RIfS), biomolecular reactions happen on the sensing component. The sensing component is a glass slide adjusted with a thin layer of translucent dielectric material (e.g., SiO2, SiO2–Ta2O5). When the white light strikes the reverse side of the glass, an intervention occurs from the partial beams, reflected at each interface. This intervention alternates maximum and minimum reflectance range [50], which corresponds to the constructive and destructive reflected radiation interference. Biomolecular reactions cause build-up of an adlayer on top of the dielectric, which increases the optical path length. This results in a reflectance spectrum change [51]. This change can be associated with the intensity of the reacting biomolecules and is equivalent to the increase in thickness. Information about the viscosity and refractive index of the adsorbed protein layer is given by alterations in the polarized light phase and amplitude. For the identification and quantification of diclofenac in bovine milk, this approach was used, and the detection limit obtained was 0.112 μg.

## **5.5 Surface-enhanced Raman scattering**

Surface Enhanced Raman scattering (SERS) spectroscopy method are used for the extremely sensitive biological analytes. With rapid growth during the last four decades, surface-enhanced Raman scattering has become one of the most reliable spectroscopic method. Applications for (SERS) detection are expanding quickly in various fields such as materials science, chemistry, biochemistry, and life sciences. Remarkable growth has resulted in biological and biomedical sensing applications from advances in the creation and production of SERS-based biosensors particularly. Electromagnetic improvement leads primarily to SERS improvement, and the configurations of the hotspot are essential to the success of responsive and reproducible detection [52]. Biosensors that are SERS-based can be generated according to the sensing requirements through direct and indirect methods. To define SERS, it is an extremely sensitive optical detection method using lasers in molecules adsorbed on the top of a metal nanoparticle in order to excite vibrational transitions. The Raman cross-section for a molecule on a surface is enhanced by factors of 10 caused by large optical fields. Because of molecular vibrational events, Raman scattering depends mainly on the loss (Stokes) or gain (anti-Stokes) of energy; from inflexible scattered photons and represents the information on the molecular structure, allowing in situ and real-time detection [53, 54]. SERS is a subclass of

Raman dispersion and provides a million-fold improvement by plasmonic nanostructures, making the sensitivity of detection down to the level of a sole molecule as can be seen in **Figure 7**.

#### **5.6 Surface plasmon resonance (SPR)**

The first observation of SPR physical phenomenon was in 1902. Through decades, this observation of an esoteric optical phenomenon developed into a complete comprehension of surface plasmon physics. Then, the first successful usage of SPR was in 1983 through the fabrication of an SPR-based sensor to detect the interactions of bimolecular. Pharmacia Biosensor AB was launched the first commercial SPR-based biosensor device, which was renamed as Biacore later. Currently, several manufacturing are fabricating SPR devices. Moreover, nowadays, the SPR-based biosensor is the dominant method of biosensing [56, 57].

The SPR appears on that surface of the device, when a polarized light such as Laser or LED is illuminated to the metal surface (usually gold or silver coated service) at a particular angle and at the interface of two media (commonly water and glass). This led to the surface plasmons generation and thus a reflected light intensity reduction is created at a particular angle known as the resonance angle. This impact is proportional to the mass on the surface. To obtain a sensogram, the shift of reflectivity, wavelengths or angle are measure against time. In all configuration, label-free, direct and real-time changes of refractive index is enabled by the phenomenon of SPR at the surface of sensor, in which it is proportional to the concentration of the biomolecule as shown in **Figure 8** [58].

#### **5.7 Liquid sensor based on optical surface plasmon resonance**

With the widespread and increased demand of biological sensing devices, there has been a considered attention on reliable and multipurpose biomolecule detection systems. The motivation to produce these detection systems become greater due the rising of health awareness and spread of aging in world population. The affinitybased biosensors, which consists of a biological element and a transducer, is one of the well-known biological agent sensing devices. In the biosensor, the biological element is typically used to identify the substance that necessarily must be detected. While the transducer is used to convert the energy from one form to another, which means converting the event of bio- recognition into an electrical signal that is measurable [59, 60].

Different types of transducers for biosensors are available currently; some of them are piezoelectric transducer, optical transducer and electrochemical transducer. Optical methods have become the most know method among these transducers, which are: surface plasmon resonance (SPR) spectroscopy, interferometry, fluorescence spectroscopy and evanescent wave-based detection. In the past years, the fluorescence-based detection methods, such as Enzyme-Linked Immunosorbent Assay (ELISA), have been implemented due to their capabilities of high throughput for samples and device sensitivity. But recently the new detection methods require processing of time-consuming labeling with several procedures of protocol detection. Detection systems based on the technology of SPR based bimolecular detection have been commercialized successfully regardless of their novelty. In addition, this method simplifies real-time controlling with high sensitivity without requiring any procedures of labeling. Nevertheless, the current implemented and commercial SPR sensors are comparatively massive size systems and have low throughput, in which they limit their applications range. Hence, higher throughputs are needed

**25**

unit [56–59, 64].

*Optoelectronics and Optical Bio-Sensors DOI: http://dx.doi.org/10.5772/intechopen.96183*

problems have solved partially [56, 61–64].

**6. SPR fabrication**

**Figure 8.**

**Figure 7.**

with additional disposable and compact SPR system, even though that some of their

*The schematic of the working principle of SPR and the steps of the SPR analytical cycle.*

*(A) SERS substrate modification by antitarget antibody, (B) target isolation, followed by binding of* 

*nanoparticles (NPs), (C) labeled by SeRS tag, and SeRS-tag detection [55].*

This section and all the fabrication and results have been achieved previously by MQW Group at UCF [56–59, 64]. In this work, a sensor head of optical surface plasmon resonance (SPR) has illustrated in this work. It depends on an inverted-rib dielectric waveguide. The changes happen at the gold metaldielectric interface, in which the resonance wavelength of the surface plasmon is excited. These changes are in relationship with the environment changes that occur at the top metal surface. The sensor head of the SPR with the inverted-rib dielectric waveguide composed of SU-8 polymer layer with 1.5 refractive index, whereas the cladding lower layer contains silicon oxynitride (SiOxNy) with 1.526 refractive index. The top layer is painted with a 50 nm gold thick layer. The design of sensor head of the SPR permits controlling the media of analyte with 1.44 to 1.502 refractive index. By using reference liquids collection that represent the analyte medium, an analyzer of optical spectrum and a broadband light source were utilized to measure the SPR sensor sensitivity. It was realized that when a liquid contacts the gold metal with 1.442 refractive index, the transmission spectrum has a sharp resonance dip at 1525 nm and with using a liquid of 1.502, its position was shifted to 1537 nm. Therefore, based on these measurements, the sensor devices sensitivity was specified to be S = 232 nm.RIU-1. In this section, we demonstrate that the device can be integrated completely with a photodetection unit, a wavelength tunable light source and a liquid delivery system through microfluidic channels to make it an extremely compact

#### **Figure 7.**

*Optoelectronics*

as can be seen in **Figure 7**.

**5.6 Surface plasmon resonance (SPR)**

biosensor is the dominant method of biosensing [56, 57].

concentration of the biomolecule as shown in **Figure 8** [58].

**5.7 Liquid sensor based on optical surface plasmon resonance**

Raman dispersion and provides a million-fold improvement by plasmonic nanostructures, making the sensitivity of detection down to the level of a sole molecule

The first observation of SPR physical phenomenon was in 1902. Through decades, this observation of an esoteric optical phenomenon developed into a complete comprehension of surface plasmon physics. Then, the first successful usage of SPR was in 1983 through the fabrication of an SPR-based sensor to detect the interactions of bimolecular. Pharmacia Biosensor AB was launched the first commercial SPR-based biosensor device, which was renamed as Biacore later. Currently, several manufacturing are fabricating SPR devices. Moreover, nowadays, the SPR-based

The SPR appears on that surface of the device, when a polarized light such as Laser or LED is illuminated to the metal surface (usually gold or silver coated service) at a particular angle and at the interface of two media (commonly water and glass). This led to the surface plasmons generation and thus a reflected light intensity reduction is created at a particular angle known as the resonance angle. This impact is proportional to the mass on the surface. To obtain a sensogram, the shift of reflectivity, wavelengths or angle are measure against time. In all configuration, label-free, direct and real-time changes of refractive index is enabled by the phenomenon of SPR at the surface of sensor, in which it is proportional to the

With the widespread and increased demand of biological sensing devices, there has been a considered attention on reliable and multipurpose biomolecule detection systems. The motivation to produce these detection systems become greater due the rising of health awareness and spread of aging in world population. The affinitybased biosensors, which consists of a biological element and a transducer, is one of the well-known biological agent sensing devices. In the biosensor, the biological element is typically used to identify the substance that necessarily must be detected. While the transducer is used to convert the energy from one form to another, which means converting the event of bio- recognition into an electrical signal that is

Different types of transducers for biosensors are available currently; some of them are piezoelectric transducer, optical transducer and electrochemical transducer. Optical methods have become the most know method among these transducers, which are: surface plasmon resonance (SPR) spectroscopy, interferometry, fluorescence spectroscopy and evanescent wave-based detection. In the past years, the fluorescence-based detection methods, such as Enzyme-Linked Immunosorbent Assay (ELISA), have been implemented due to their capabilities of high throughput for samples and device sensitivity. But recently the new detection methods require processing of time-consuming labeling with several procedures of protocol detection. Detection systems based on the technology of SPR based bimolecular detection have been commercialized successfully regardless of their novelty. In addition, this method simplifies real-time controlling with high sensitivity without requiring any procedures of labeling. Nevertheless, the current implemented and commercial SPR sensors are comparatively massive size systems and have low throughput, in which they limit their applications range. Hence, higher throughputs are needed

**24**

measurable [59, 60].

*(A) SERS substrate modification by antitarget antibody, (B) target isolation, followed by binding of nanoparticles (NPs), (C) labeled by SeRS tag, and SeRS-tag detection [55].*

**Figure 8.** *The schematic of the working principle of SPR and the steps of the SPR analytical cycle.*

with additional disposable and compact SPR system, even though that some of their problems have solved partially [56, 61–64].
