62 S. Suresh and P. Mathan

L&4F1>354'DE4I5>D5B? D4

Rev. Adv. Mater. Sci. 36 (2014) 62-69

Corresponding author: Suresh Sagadevan, e-mail: sureshsagadevan@yahoo.co.in

RECENT TRENDS IN NANOBIOSENSORS AND THEIRAPPLICATIONS - A REVIEW

Suresh Sagadevan1 and Mathan Periasamy2

1Department of Physics, Sree Sastha Institute of Engineering and Technology, Chembarambakkam,Chennai-600 123, India

2Department of Biotechnology, Sree Sastha Institute of Engineering and Technology, Chembarambakkam,Chennai-600 123, India

Received: May 30, 2013

Abstract. Nanotechnology plays an important role in the development of biosensors. The sensitivityand performance of biosensors are improved by using nanomaterials through new signaltransduction technologies. The development of tools and processes used to fabricate, measureand image nanoscale objects, has led to the development of sensors that interact with extremelysmall molecules that need to be analyzed. These advances are particularly exciting in the contextof biosensing, where the demands are for low concentration detection and high specificity. Theuse of biomolecule-functionalized surfaces can drastically boost the specificity of the detectionsystem, but may also pose reproducibility problems and increased complexity. Severalnanobiosensor architecture-based mechanical devices, optical resonators, functionalizednanoparticles, nanowires, nanotubes, and nanofibers have been in use. As nanobiosensortechnology becomes more refined and reliable, it will eventually make lab-on-a-chip devices forrapid screening of a wide variety of analyses at low cost. In particular, nanomaterials such asgold nanoparticles, carbon nanotubes, magnetic nanoparticles and quantum dots have beenactively investigated for their applications in biosensors, which have become a new interdisciplinaryfrontier between biological detection and material science. This paper reviews the status of thevarious nanostructure-based biosensors and their applications.

1. INTRODUCTION

A biosensor is a device that combines a biologicalrecognition element with a physical or chemicalDB1>C4E35BD?45D53D129?

63Recent trends in nanobiosensors and their applications - a review

body fluids, and food and environmental samples[4]. Researchers tend to integrate nanoparticles intothe materials used for biosensor construction, inorder to improve the performance of the system inboth the existing and potential sensing applications.This paper reviews the major aspects of thenanotechnology-based biosensors, theirapplications in various fields and addresses the need

Fig. 1. Biosensors; an excellent example of multi and interdisciplinary research area.

Fig. 2. Components of a typical biosensor.

for fundamental and continued research for furtherdevelopment.

2. NANOBIOSENSORS

Nanotechnology is a new branch of science thatdeals with the generation and alteration of materialsto nanosize (10-9 m). Various nanomaterials have

64 S. Suresh and P. Mathan

Fig. 3. Different field applications of nanobiosensors.

been discussed to analyze their properties and re-cent applications in biosensors [5]. The research inbiosensor technology shows a constant increasein relation to the various nanomaterials with theinterest to be implemented either into transducersor receptors operation parts, so as to enhance theirmultidetection capability and sensitivity. Thesenanomaterials are nanoparticles, nanotubes,quantum dots or other biological nanomaterials.These nanomaterials can contribute to either thebio-recognition element or the transducer or both,?6129?C5>C?B531EC5?6D859BCE2=93B?>C9J5nanosensors, nanoprobes and other nanosystemshave revolutionized in the fields of chemical andbiological analysis, to enable the rapid analysis ofmultiple substances in vivo. In recent years, a widevariety of nanoparticles with different properties, suchas small size, high speeds, smaller distances forelectrons to travel, lower power, and lower voltages,81F56?E>42B?141]]9>29?C5>C?BC/0Important advances in the field of nanotechnologyhave led to the utilization of nanomaterials such asmetal nanoparticles [7], oxide nanoparticles [8],magnetic nanomaterials [9], carbon materials[10,11], Quantum Dots [12] andmetallophthalocyanines [13] to improve the

electrochemical signals of biocatalytic events thatoccur at the electrode/electrolyte interface.Functional nanoparticles that bound to biologicalmolecules (e.g. peptides, proteins, nucleic acids)have been developed for use in biosensors to detect1>41=]1

65Recent trends in nanobiosensors and their applications - a review

significantly affect the bulk electrical properties ofthe structure. Due to their small size, nanomaterialsmay be taken up by cells [16-18], and thus arepromising candidates for in vivo sensingapplications. In some cases, the inherent electricalproperties of the device, such as carbon nanotubes,are particularly extraordinary and lend themselvesto improved sensor sensitivity. Several sensingplatforms have been developed with nanomaterialsthat exploit a change in output signal [19].Nanobiosensors are categorized based on thesenanomaterials, and play a vital role in different fields,as shown in Fig. 3.

4. NANOPARTICLES-BASEDBIOSENSORS

Metallic nanoparticles are very interesting materialswith unique electronic and electrocatalytic propertiesdepending on their size and morphology [20,21].Nanoparticle-based biosensors are particularlyattractive because they can be easily synthesizedin bulk using standard chemical techniques, anddo not require advanced fabrication approaches.They also offer particularly high surface areas dueto their extremely small size and are typically usedas suspensions in solutions (during the time whenthey interact with the analyse). Most biologicalmolecules can be labelled with metal nanoparticleswithout compromising their biological activities [22].In particular, gold nanoparticles are much exploredmaterials as components for biosensors, due to theircapability to increase an electronic signal when abiological component is maintained in contact withits nanostructured surface [23]. The exploration ofgold nanostructured materials has provided newpaths for enzymatic biosensor development. Gold

Fig. 4. Magnetic nanoparticle based biosensor.

nanoparticles also greatly improve the electron trans-fer across the monolayer molecules self-assembledon the surfaces of electrodes [24]. This observationis especially useful in the development of electrolu-minescence-based biosensors [25]. Apart from gold,silver, platinum, palladium, copper, cobalt and othernanoparticles are also extensively explored in thedevelopment of biosensors [22, 27-29].

Gold nanoparticle modified DNA has been usedto develop a microcantilever-based DNA biosensor[30] (Su et al.) to detect DNA even at very lowerconcentration through a hybridization reaction. Thisreaction leads to the attachment of goldnanoparticles, and acts as a nucleating agent forthe growth of silver particles when exposed to aphotographic developing solution. The growth of silverparticles increased the effective mass of themicrocantilever and led to an enhanced frequencyshift. This method could detect the target DNA at aconcentration of 0.05 nM or lower. Microcavityresonators made of porous silicon have been usedin biosensors. These resonators possess the uniquecharacteristics of line narrowing and luminescenceenhancement. Porous silicon has been used as anoptical interferometric transducer for detecting smallorganic molecules, such as biotin and digoxigenin,16-nucleotide DNA oligomers, and proteins(streptavidin and antibodies) at pico- and femtomolarlevel concentrations [31].

Magnetic nanoparticles are always powerful andversatile diagnostic tools in biology and medicine.A new technique has been introduced for the rapiddetection of biological targets by using superparamagnetic nanoparticles based on a high-transition temperature DC SuperconductingQuantum Interference Device (SQUID) [32]. In thistechnique, a Mylar film with a bound target is placed

66 S. Suresh and P. Mathan

Fig. 5. Carbon nanotubes based biosensor.

on the microscope. A suspension of magneticnanoparticles carrying antibodies is added to themixture in a well, and 1-s pulses of magnetic fieldare applied parallel to the SQUID. In the presenceof this aligning field, the nanoparticles develop a netmagnetization, which relaxes when the field is turnedoff. Unbound nanoparticles relax rapidly by Brownianrotation, and contribute no measurable signal.Nanoparticles bound to the target are captured andundergo Neel relaxation, producing a slowlydecaying magnetic flux, which is detected by theSQUID. The working mechanism of the SQUID isdiagrammatically represented in Fig. 4.

Nanowire biosensors can be decorated withvirtually any potential chemical or biologicalmolecular recognition unit, through convenientsurface properties. The nanomaterials transduce thechemical binding event on their surface into a changein the conductance of the nanowire in an extremelysensitive, real time and quantitative fashion. Boron-doped silicon nanowires (SiNWs) have been usedto create highly sensitive, real-time electricity basedsensors for biological and chemical species. Biotin-modified SiNWs were used to detect streptavidindown to at least a picomolar concentration range.The small size and capability of these semiconductornanowires for sensitive, label-free, real-time detectionof a wide range of chemical and biological speciescould be exploited in array-based screening and invivo diagnostics.

5. CARBON NANOTUBE-BASEDBIOSENSORS

Carbon materials have received great attention inthe last two decades with the emergence ofnanoscience [33]. These include the modificationof electrodes with different nanocarbons, such ascarbon powder, carbon nanotubes, graphene sheetsand carbon capsules [34-36]. The investigation of

the electronic properties of carbon nanotubes byIijima and co-workers [38] is one of the most reportedapproaches to explain their detection capability.Carbon nanotubes (CNT) are formed by a hollowcylinder of a unique carbon sheet with a single walledcarbon nanotube (SWCNT) or concentric carbonsheets of different diameters forming multiwalledcarbon nanotubes (MWCNT) with sp2 bonding [33].The particular cylindrical form of CNT is the principalaspect that provides the quantum confinement effectin the oriented 1D nanostructured materials [38].These characteristics provide the possibility toincrease the chemical reactivity and electronicproperties of this particular carbon material, whichbecomes a crucial point for biosensing devices [35].

Recent studies have established the fact thatCNT can enhance the electrochemical reactivity ofimportant biomolecules [39,40], and can promotethe electron-transfer reactions of proteins [41,42].In addition to enhanced electrochemical reactivity,CNT-modified electrodes have been shown to beuseful in accumulating important biomolecules (e.g.,nucleic acids) [43], and alleviating surface foulingeffects [40]. The remarkable sensitivity of CNTconductivity to the surface adsorbates permits theuse of CNT as highly sensitive nanoscale sensors.These properties make CNT extremely attractive fora wide range of electrochemical biosensors rangingfrom amperometric enzyme electrodes to DNAhybridization biosensors. To take advantage of theremarkable properties of these unique nanomaterialsin such electrochemical sensing applications, theCNTs need to be properly functionalized andimmobilized. Among the many potentialapplications, carbon nanotubes have recentlybecome promising functional materials for thedevelopment of advanced biosensors, such asamperometric and potentiometric biosensors, thatare represented in Fig. 5.

67Recent trends in nanobiosensors and their applications - a review

6. BIOLOGICAL NANOMATERIALS-BASED BIOSENSORS

In a biosensor, the bioreceptor is combined with asuitable transducer which produces a signal afterinteraction with the target molecule of interest. Thepresence of the biological element makes thebiosensor systems extremely specific and highlysensitive, giving an upper edge over the conventionalmethods. Over the years, a number of differentnatural and artificial biological elements have beenused in biosensors; the most important ones areenzymes, dendrimers, thin films etc. In enzyme-based biosensors, the biological element is theenzyme which reacts selectively with its substrate[44]. Enzymes are the most used biocatalyticelements, enabling the detection of analyses invarious ways. Since enzymatic reactions arefollowed by the consumption or production of variousspecies, transducers can easily detect as well ascorrelate these consumed or produced species tothe substrates.

Dendrimers are known as organicmacromolecules with tridimensional and highlydefined structure functionality [45]. The capabilityof these dendrimeric structures to stabilize andmaintain the integrity of metallic nanoparticles wasreported by Crooks [46]. The development ofmicroelectrodes for the measurement of oxygen andhydrogen peroxide concentration is based on siliconsubstrate utilization through microfabricationtechnology. Enzymes or microorganisms are fixedon these oxygen-sensing chips by the use ofphotoresists. Thin nanostructured films have openedthe possibility, to fabricate biosensors with a highpower of detection, with intrinsic propertiesassociated with their dimensions at the nanoscalelevel [47]. These interesting properties can beexplained at the organizational level, when amolecular arrangement is obtained at a solidconductor substrate. Moreover, the possibility toimprove the detection limit in biosensing devicescan also be explained, by using compatiblematerials such as natural polymers.

7. CURRENT TRENDS INNANOBIOSENSORS

There is a big demand for fast, reliable and low-costsystems for the detection, monitoring and diagnosisof biological molecules and diseases in medicine[48,49,1]. Of course, this demand is not restrictedonly to the field of medicine; it exists in the areas ofenvironmental pollutant monitoring, detection of food

borne pathogens, and the potential danger ofbioterrorism. The development of ultra-sensitivebiological and chemical sensors is one of the grandscientific, engineering, and educational challengesof the 21st century. The next generation biosensorplatforms require significant improvements insensitivity and specificity, in order to meet the needsin a variety of fields including in vitro medicaldiagnostics, pharmaceutical discovery andpathogen detection. Advances in diagnostictechnology have been essential to the progress ofmedicine. The ability to identify diseases andpathogens by detecting associated proteins, nucleicacid sequences, organelles, cell receptors,enzymes, and other markers, can provide biomedicalresearchers and healthcare professionals with adetailed knowledge of disease pathways and patientsconditions. However, many of the conventional testscurrently available are slow, and require largeamounts of sample materials, and may lead to falsepositive or negative results. Thus, there is a needfor rapid, trustworthy, low-cost, multiplexed screeningto detect a wide range of biomaterials. The currentstate-of-the art diagnostic biosensors are based onseveral technologies, often including either theenzyme-linked immunosorbent assay (ELISA), oramplification of a sample by polymerase chainreaction (PCR), using appropriate primers anddetection methods. The research onnanobioelectronics & biosensors aims at theintegration of nanoelectronics, tools and materialsinto low cost, user friendly and efficient sensors andbiosensors, with interest in several fields such asdiagnostics, food analysis, environment monitoringand other industries.

8. CONCLUSION

Nanotechnology is revolutionizing the developmentof biosensors in recent years. Nanobiosensorresearch focuses on developing innovativetechnologies that have the ability to make significantcontributions in the areas of human and animaldisease marker detection, promising therapeuticcompound identification and analysis, nano-andbiomaterials characterization, and biocatalystdevelopment. These technologies take the form ofnanometrically engineered, biologically activesurfaces, or liquid-solid interfaces, and the toolsnecessary to characterize them. The emergence ofnanotechnology has opened up new horizons forthe development of nanosensors and nanoprobeswith submicron-sized dimensions, that are suitablefor intracellular measurements.The attention is being

68 S. Suresh and P. Mathan

focussed on the study of various nanoeffects, suchas the quantum size effect, mini size effect, surfaceeffect, and the macro-quantum tunnel effect, that isunique to nanomaterials, and is actually their mostattractive aspect. New nanomaterials andnanostructures need to be explored for use inbiosensors. Preferably, nanotechnology-basedbiosensors should be integrated within tiny biochipswith on-board electronics, sample handling andanalysis. This will greatly enhance their functionality,by providing devices that are small, portable, easyto use, low cost, disposable, and highly versatilediagnostic instruments. Laser nanosensors can beused for the in vivo analysis of proteins andbiomarkers in individual living cells.

Even though a wide range of nanobiosensorshave been developed in the past two decades, thefuturistic goal of low-cost, high throughput,multiplexed clinical diagnostic lab-on-a-chip devicesis yet to be truly realized. It is still unclear whichnanobiosensor architectures are best matched towhich diagnostic tasks. Moreover, nanobiosensorsthat are functional in the lab may not be of use inthe field or clinic for several reasons. Well-structuredinterdisciplinary research programs that involve, lifescience researchers, engineers and physicians haveto be conducted, to reveal more refined and affordablebiosensors.

ACKNOWLEDGEMENTS

The authors thank the Management, Principal andFaculty members of Sree Sastha Institute ofEngineering and Technology, Chembarambakkam,Chennai-600123, for their constant encouragementand support throughout this work.

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