Nanotechnology can be termed as the design, production and application of constructions, devices and systems by controlled direction of size and form at the nanoscale that produces constructions, devices and systems with at least one new belongings ( 1 ) .
1 nanometre is one billionth of a metre. The physical and chemical belongingss of stuff get changed significantly at nanoscale. For e.g. Metallic elements with mean size of 10 nanometers are significantly harder and tougher when compared to hardness and toughness at the size of 1000 nanometer. This difference in belongingss is ascribed to two chief grounds ( 2 ) :
1. Nanomaterial has big surface country when compared to same mass in larger signifier. This makes it extremely reactive and has an consequence on the stuff ‘s strength and electrical belongingss ( 2 ) .
2. Quantum effects begin to increase with lessening in size which has an impact on optical, electrical and magnetic belongingss of stuff ( 2 ) .
Nanotechnology has many applications such as nanomedicine, nanofluidics, molecule ego assembly, intelligent drug bringing systems, nanomachines. One of these is nanobiosensors ( 2 ) .
Components of nanobiosensors:
They are made up of 3 parts ( 3 ) :
sensitive biological component:
These can be either populating biological stuffs ( for ex. Microorganisms, cell receptors etc. ) or biological molecules ( for ex. Organelles, enzymes, feeling variety meats, antibodies, man-made receptors, nucleic acids etc. )
The transducer ( 4 ) :
It measures the physical alteration due to the reaction of sensitive biological component with bioreceptor. They work straight or indirectly depending upon which biosensors are classified as:
Direct sensing biosensors: the biological reaction can be straight measured. E.g. biosensors utilizing antibodies or cell receptors ( i.e. non catalytic ligands ) .
Indirect sensing biosensors: the biological reaction is detected by secondary sensor. E.g. labeled antibodies, catalytic enzymes.
Signals from the transducer are amplified, analyzed, converted to concentration units and so stored in storage device.
Techniques of bring forthing nanomaterials:
There are two techniques ( 5 ) of bring forthing nanomaterials. They are:
Top down techniques
Bottom up techniques
Top down technique produces really little constructions from larger 1s while ‘bottom up technique ‘ concepts nanomaterials by fall ining atom by atom or molecule by molecule. In underside up technique, nanomaterials can be produced either by ego assembly, in which atoms or molecules get arranged due to their natural belongingss or by positional assembly, in which tools are used to travel each atom or molecule separately. However, the latter method is boring and non suited for industrial applications.
Nanomaterials can be produced in one, two or three dimensions ( 5 ) .
Nanomaterial in one dimension:
These include thin movies and engineered surfaces which have been developed and used for decennaries. For e.g. in Si integrated circuit industry many devices depend on thin movies for their operation. Progresss are being made to command the composing and smoothness of surfaces ( 5 ) .
Nanomaterials in two dimensions:
These include nanotubes and nanowires. These have generated involvement among the research workers in past few old ages ( 5 ) .
C nanotubes ( CNTs ) :
These were foremost observed by Sumjo lijima ( 7 ) in 1991. CNTs ( 5, 6 ) may be individual walled ( one tubing ) or multiwalled ( several concentric tubings ) . CNTs are few nanometres in diameter and several nanometres to centimetres long. These have gained a batch of importance in nanoworld because of their high mechanical strength ( Young ‘s modulus over 1 i.e. every bit difficult as diamond ) , flexibleness and good electrical conductance ( 2, 5 ) .
These are based on superimposed compounds such as Mo disulfide, Si ( 5, 8 ) . They have first-class lubricator belongingss, opposition to shockware impact, catalytic responsiveness and high capacity for H and Li storage ( 5 ) .
These are ultrafine wires or additive arrays of points formed by ego assembly. These semiconducting material nanowires are made from a broad scope of stuffs like Si, Ga nitride, indium phosphide etc. they have singular optical, electrical and magnetic belongingss. These are prepared by ego assembly techniques. Nanowires have broad applications in high denseness day of the month storage, either as magnetic read caputs or every bit patterned storage media and electronic and opto electronic nanodevices for metallic interconnects of quantum devices and nanodevices ( 2, 9 ) .
Biopolymers such as Deoxyribonucleic acid molecules can be coated in metal. The ego assembly of organic anchor nanostructures is controlled by weak interactions like H bonds, hydrophobic or new wave der waal ‘s interactions ( by and large in aqueous environment ) and therefore requires rather different synthesis schemes to CNTs ( 5 ) .
Nanomaterials in three dimensions:
nanoparticles have diameter less than 100 nanometers. These exhibit new or enhanced size dependent belongingss compared with big atoms of the same stuff. Nanoparticles serve as the natural stuffs, ingredients or additives in assorted merchandises ( 5, 10 ) .
fullerenes ( C60 ) :
In the mid of 1980, Kroto and Richard Smalley discovered a new category of C compounds carbon 60 and named it “ buckminsterfullerene ” ( 11 ) . C60 are spherical molecules about 1nm in diameter. They are applied as illumination ball bearings to lubricate surfaces, drug bringing vehicles and electronic circuits ( 5 ) .
Dendrimers are spherical polymer molecules formed through ego assembly procedure. These are used in coatings and inks. They can besides be used as nanoscale bearer molecules in drug bringing ( 5, 12 ) .
If semiconducting material atoms are made little plenty, quantum effects begin to rule. There is alteration in chemical, optical and electrical belongingss. Such nanoparticles are called quantum points ( 5 ) .
Many nanobiosensors have been developed. Some of them are as follows ( table 1 ) :
Colorimetric: coloring material alterations
Photometric: light strength alterations
Diagnosis of malignant neoplastic disease, direct glucose degree sensing in blood
( 13, 14, 15 )
Based on alterations in electric alterations
Label free DNA sensing, diagnosing of different diseases
( 16 )
Sensitive biomolecules immobilized
Electrochemical sensing of blood glucose degrees, finding of DNA and its effecters
( 17, 18 )
Deoxyribonucleic acid nanobiosensors
Hybridization of nucleic acids from different beginnings
Detection of cistrons and mutant cistrons related to inherited human diseases
( 18, 19, 20 )
Used in topographic point of ELISA- based methods, betterment over PCR based sensing, cheaper, faster method
( 21 )
Sensitive biomolecules immobilized
Used for immunochemical assay, malignant neoplastic disease diagnosing and therapy, diagnosing of Alzheimer ‘s disease
( 22, 23 )
Sensitive biomolecules immobilized
Diagnosis of malignant neoplastic disease, drug find, intervention of diseases, kinetic surveies of cardinal biochemical reactions
( 24 )
Nanotube based nanobiosensors
Carbon nanotubes used every bit electrodes every bit good as immobilisation stage
Used in immunochemical assaies, nucleic acid investigation checks, clinical chemical science checks
( 25, 26, 27 )
Some of the nanobiosensors and rule behind their working are described below:
Fluorescent nanobiosensors for enzymatic activity sensing based on liposomes:
Liposomes are nanoscale spherical shells which consist of lipid bilayers with aqueous stage indoors. They can be easy formed and they are stable for drawn-out period without important differences in size and construction ( 28 ) . They have biocompatible microenvironment and their physicochemical belongingss can be controlled. They can be efficaciously used as bearers for many functional substances and drugs. Release of these substances from liposomes can be controlled based on their physicochemical belongingss. Enzymes can be well protected from blossoming and from the onslaught of outer agents like peptidases inside the microenvironment of liposomes. Enzymes embedded in lipopsomes can keep their activity at low concentration ( 29 ) . Liposomes are optically transluscent and therefore can be employed for the formation of nanosized optical biosensors under specific experimental conditions. Initially liposome based electrochemical biosensors were developed with glucose oxidase ( 30, 31 ) on screen printed electrodes ( 32 ) and on chitosan gel beads ( 33 ) . Porins can be entrapped within liposomes which facilitate incorporation of enzyme molecules in the internal aqueous stage of liposomes. Sensitive transduction can be achieved with the aid of pH sensitive fluorescence investigation ( 34 ) which is inserted within liposome. This provides a simple ego contained stable nanobiosensor.
The porins incorporated on liposome membrane allow substance ‘s entry in the internal microenvironment of the liposome where they can respond with enzyme. Change in the pH leads to alter in the coloring material of fluorescent index. This alteration is straight relative to substrate concentration. Due to fluorescence it is easy to obtain higher sensitiveness, lower sensing bounds and wider concentration scope ( 34 ) . Incorporation of fluorescent index within nanobiosensor avoids two measure sensing of enzyme activity ( 34 ) . A crisp fluorescent signal is obtained when substrate is added to the enzyme incorporating liposome. Increase in the substrate concentration is reciprocally relative to strength of fluorescence. Liposomes are really little and non easy to manage. Therefore they are immobilized in a colloidal suspension gel matrix. This matrix does non present mistakes in the fluorescent signals by organizing an extra diffusion barrier or does non impact enzme dynamicss. These nanobiosensors can be employed in the sensing of organophosphorus pesticides and other toxic AchE inhibitors ( 34, 35 ) .
Organophosphates are the most widely used pesticides due to their ability of rapid insect irradication, short environmental half life. They are extremely toxic and exert many sick effects on CNS, respiratory, myocardial and neuromuscular malfunction which may take to decease. Their residues are found in the dirt, atmosphere, and agricultural merchandises every bit good as in land H2O ( 35 ) .
They are structural parallels of Ach and irreversibly suppress Ach ( 35 ) . They block active site on AchE ; prevent the binding of Ach and its interruption down to choline and acetic acid. This decreases acetic acid production ( 35, 36 ) . The fluorescence signal of fluorescent index lessenings. The decrease in response is correlated with concentration of pesticide in solution.
Glucose biosensors utilizing protein immobilized within gold/ polycarbonate nanopores:
The glucose galactose receptor ( GGR ) protein belongs to bacterial periplasmic protein ( bPBP ) superfamily. It is used as biorecognition component in glucose biosensors. It is preferred as the active constituent of glucose biosensors ( 38, 39 ) because it has high solubility and stableness upto 600C. These proteins undergo big physiological alteration i.e. broad amplitude, flexible joint turn gesture upon adhering to the glucose. This alteration can be detected utilizing assorted analytical techniques such as fluorescence, quartz- crystal microbalance, electrochemical electric resistance and surface plasmon resonance sensing. One of these methods is immobilising this receptor protein within Au/ polycarbonate nanopores ( 38, 39 ) . The gold nanoisland is prepared with the aid of polycarbonate Au templet.
The original GGR protein does non incorporate cysteine residues. These cysteine residues are incorporated by familial technology. Immobilization of these proteins occurs due to Au-S bond formation ( 40 ) .
The cells consist of two Polytetrafluoroethylene blocks with cylindrical dullard in between. Fluid recess and mercantile establishment are present on both the sides to quickly run out the electrolyte. The Au coated electrolyte is mounted between two Teflon blocks. One electrode acts as working electrode while the other serves as both mention every bit good as music director electrode. The electric resistance obtained is straight relative to the opposition or reciprocally relative to the conduction between two electrodes. ( R=1/C ) . Electric resistance decreases with increased glucose concentration. The greatest truth in the measuring of electric resistance is obtained when the diameter of the nanopores is smallest. This method provides an alternate reagentless biosensor for sensing and measuring of glucose biosensors. Glucose adhering to protein is detected as an addition in electrolyte conduction as an addition in the electrolyte conduction within the nanopores caused by decrease in the effectual protein movie thickness. Hence its concentration can be determined ( 41 ) .
Optical nanobiosensors for intracellular or subcellular analyte sensing:
PEBBLEs ( Probe Encapsulated By Biologically Localized Embedding ) are single-channel or multicomponent spherical devices of nano size made up of detectors entrapped in inert chemical matrix. They occupy every bit little as 1 ppm of the cell ‘s volume ( 42 ) . Small size of detectors has many advantages ( 43 ) such as accurate sensing of intracellular analyte, greater declaration of chemical images, lower sensing bounds and rapid response. These are used for existent clip detection of ions and little molecules. Inert matrix prevents protein binding of detectors ( for e.g. non specific protein binding of dyes ) and besides protects cellular constituents from harmful effects of chemical detectors ( 42 ) . Depending upon the type of detector stuff, three different matrices are used: hydrophilic, hydrophobic, amphilic. There is a really small or no photobleaching and leaching of dyes. These PEBBLEs can be used singly or in group of individual analyte PEBBLEs or sets of multi analyte PEBBLEs or “ ensembles ” of sets of groups. “ Esembles ” enable either multi analyte sensing or coincident chemical images of complex cellular biochemical procedures. These can be inserted into the cell utilizing a cistron gun, microprojector, biolistics, as liposomes or by natural consumption ( phagocytosis ) ( 41 ) .
Advantages of these PEBBLEs are:
They allow sensing of intracellular analytes for which no intracellular fluorescent indexs are available. For e.g. Na, nitrite, chloride etc.
It is possible to distinguish between the fluorescence of the index and fluorescence of intracellular cell organs of the cell. These PEBBLEs can be employed for the sensing of Mg, K, Ca, O and pH alterations due to cellular alterations ( 41, 44 ) .
Development of nanobiosensors for supervising single cells: *
Heat and draw technique is used in this method. In this technique, a silica optical fiber is fitted into a fibre pulling device at both the terminals. It is heated at the center utilizing a CO2 optical maser or a heat fibril. The het fibril is pulled utilizing a pulling device. The form of the tip is dependent on temperature and timing of the process. One terminal of silicon oxide fiber is extremely polished which leads to excitement of negatrons to attach with biosensing component. The het surface when pulled leads to the formation of nanosized tips. These nanotips are coated within a thin bed of gold, aluminum or Ag so that the tip does non lose the aroused visible radiation. The distal terminal is left uncoated to immobilise biosensing elements like antibodies, man-made peptide substrates etc. The feeling component coupled with fluorephore is covalently bonded to uncoated terminal. The biosensor is inserted into cells utilizing assorted techniques antecedently mentioned. The fluorescence emitted is collected utilizing microscope aim and passed through dichroic mirror. It is detected with photomultiplier tubing ( PMT ) . Therefore biochemical procedures can be monitored ( 45 ) .
Electronic olfactory organs:
These have capacity of observing and separating complex odorant mixtures utilizing wide spectrum web of detectors. A characteristic response form is generated that enables designation and favoritism of odorant nowadays in the mixture. This feeling depends on assorted techniques such as electrical, optical, colorimetric, hydrometric techniques etc. to gauge parametric quantities responsible for placing odorants in the mixture. Electrical olfactory organs have specificity, stableness, objectiveness, celerity and are non hampered by the presence of H2O ( 46 ) .
Nanobiosensors and malignant neoplastic disease:
Nanobiosensors are utile for early diagnosing of malignant neoplastic disease and sensing of malignant neoplastic disease agents such as environmental pollutants, unsafe gases and pathogens. The usage of nanobiosensors in malignant neoplastic disease clinical testing have been increased due to high velocity and reduced cost for diagnosing, mechanization and multi mark analysis ( 4, 47 ) .
Antitumor drugs can be associated with nanoparticles. This avoids cellular and non cellular mechanisms of opposition, improves selectivity of drugs towards tumour cells and decreases their toxicity towards healthy tissues.
Advantages ( 48 ) of nanobiosensors in malignant neoplastic disease:
Due to extreme little size, they are easy absorbed into human organic structure.
They can easy perforate cell membrane and not risky since they are made up of biodegradable polymers.
Nanoparticles are stable and can organize colloidal scatterings.
Drugs can be adsorbed on atom surface or dissolved in atom matrix.
They can aim drugs efficaciously to tumor cells, place physiological alterations in tumour cells and detect residuary tumour cells.
They have big surface country to volume ratio which allows rapid diffusion into cells every bit good as impart high thermal and chemical opposition.
In malignant neoplastic disease intervention, detectors conjugated with biological feeling component such as malignant neoplastic disease specific antibody or other biological ligands are used to aim proteins or to prehend tumour cells. This yields electrical, optical or mechanical signals which are detected by transducer ( 49 ) . Microelectrical mechanical system detectors and quantum points have been used for DNA sensing. Recently, a method of happening specific DNA sequence by utilizing a semiconducting material crystal, biological investigations and optical maser have been developed. In this method, DNA is made to illume up beneath the microscope and so the sequence is determined.
Point of attention testing:
It is one of the hopeful methods for faster and cheaper diagnosing of malignant neoplastic disease. Cancer biomarkers are identified from genomic and proteomic analysis and validated. Probes are developed for these markers and conjugated with sensors to organize biosensors. This technique is helpful for malignant neoplastic disease attention ( 4, 47 ) .
There has been an exponential growing in the applications of nanobiosensors since last few old ages including medical specialty and wellness attention. Many nanobiosensors are available in the market based on latest engineering. In future, nanobiosensors will observe the oncoming of awful diseases like malignant neoplastic disease or bosom disease at the earliest phase possible. They are being looked as an advanced and inexpensive option to the current tendencies of diagnosing and intervention. Nanotechnology will shortly go the following frontier of medical research.