Table 3 Review of literature illustrating the nanosensors for detecting other entities

Optic particle plasmon resonance (FOPPR) immunosensor

Gold nanorods

Cymbidium mosaic virus (CymMV) or Odontoglossum ringspot virus (ORSV)

48 and 42 pg/mL for CymMV and ORSV respectively

Gold nanorods were synthesized using the seed-mediated growth method followed by their immobilization on the fiber core surface. Afterward, the AuNR surface was functionalized by antibodies through sinking the fiber in a solution of CymMV or ORSV antibody

Detection strategy is based on the localized evanescent field absorption by the AuNRs upon biomolecular binding which results in decreased transmission intensity measured at the distal end of the fiber

This nanosensor solves the problem of color interference encountered by using AuNSs, provides faster analysis, better reproducibility, and lower detection limit

[184]

Nanoparticles based immunosensor

Fe₃O₄/SiO₂

Tomato ringspot virus (ToRSV), bean pod mottle virus (BPMV) and arabis mosaic virus (ArMV)

10⁻⁴ mg/mL

Metal nanoparticles were surface modified to form amino-functionalized Fe₃O₄/SiO₂ MNPs (NH₂-Fe₃O₄/SiO₂ MNPs) followed by the covalent immobilization of antibody

There is a good linear relationship between the enhanced fluorescence and the concentrations of viruses

The target viruses can be detected by a nongrowth step

[144]

Electrochemical sensor

Multiwalled carbon nanotube

Ganoderma boninense

0.0414 mg/L

Gold (III) chloride trihydrate and sodium citrate dehydrate used for the synthesis of gold nanoparticles of different sizes and layer by layer assembly was used to modify the electrode

Electrocatalytic activities of a modified electrode towards oxidation of healthy and G. boninense-infected oil palm leaves

A sensitivity and reproducible method due to the unique characteristics of nanoparticles

[185]

Electrochemical nanosensor

TiO₂ or SnO₂ nanoparticles on screen-printed carbon (SP) electrodes

Phytophthora cactorum

35–62 nM

SnO₂ and TiO₂ were used as electrochemical detection elements for amperometric sensing and Screen-printed carbon electrodes were modified with nanoparticles of SnO₂ or TiO₂ before their use in electrochemical detection

Detection of symbolic volatile compound p-ethyl guaiacol produced during infection

Electroanalytical data obtained using cyclic voltammetry and differential pulse voltammetry exhibited that both SnO₂ and TiO₂ displayed high sensitivity

[186]

Electrochemical Biosensor

Colloidal Gold Nanoparticles

Pseudomonas syringae

214 pM

AuNPs were synthesized by the citrate reduction of HAuCl₄. The AuNP-DNA probe was prepared by adding tris(2-carboxyethyl)phosphine to DNA mixture of Pseudomonas syringae

Assessment of electrochemical changes with differential pulse voltammetry

This method can readily identify P. syringae infected plant samples even before the appearance of disease symptoms

[187]

Optical nanosensors

Selective single-walled carbon nanotube

Wound signaling

-

Cy3-labeled G-SWNT was prepared by mixing 1 mg of Cy3-ss(GT)15 and 0.25 mg of HiPCO SWNT, followed by the purification

Selective single-walled carbon nanotubes are excellent fluorescent probes that have the capability for real-time monitoring of H₂O₂ produced due to mechanical injury in plants

This nanosensor probe is independent of species and capable of real-time, spatial and temporal biochemical measurements in plants

[188]

Oxygen nanosensors

Carbon-filled quartz micropipettes having platinum-coated tips

Oxygen concentration

-

The inert carbon surface of the electrode was functionalized for the detection of redox-active species. A nanocavity was created in a carbon electrode. The fabrication of platinum nanosensors was performed in two stages: etching in alkaline solution followed by the platinization

The platinized nanoelectrode displays enhanced catalytic activity for oxygen reduction and the current of the sensor electrode was recalculated to oxygen concentration

Such novel platinum nanoelectrodes are beneficial for understanding cell oxygen metabolism

[189]

Fluorescent nanosensor

Carbon dots (CDs)

Fe³⁺

6.4 nM

CDs were synthesized from Pseudo-stem of banana plant (as carbon source) by using hydrothermal method

Drastic decrease in the fluorescence intensity of CDs upon increase in the Fe³⁺ concentration

CDs are highly selective to Fe3 + ions even in the presence of other ions

[190]

SERS-barcoded nanosensor

Au

Bacillus thuringiensis (Bt) gene transformed rice expressing insecticidal proteins

0.1 pg/mL

Encapsulation of gold nanoparticles with silica and conjugation of oligonucleotide strands for targeting DNA strands

DNA hybridization

The nanosensor provides precise detection of transgenic rice varieties

[163]

SPR nanosensor

Au

Aflatoxin B1

1.04 pg mL⁻¹

Aflatoxin and N-methacryloyl-L-phenylalanine were pre-complexed as a template molecule and functional monomer. Molecularly imprinted polymers with gold nanoparticles were coated onto surface plasmon resonance (SPR) gold chip surface

The reflectivity index in the gold electrode surface changed with the aflatoxin concentration

SPR nanosensors were have commendable selectivity and reusability

[162]