The magnetic nanoparticles also play important role in biomarker immunocapture and

detection application. The other work reported the deposition of Fe2O4 with cobalt (Co)

and Zn (CoZn-Fe2O4) nanoparticles applied in a disposable enzyme-free microfluidic

immunoarray device (µID) [23]. The CoZn- Fe2O4 nanoparticles acted as enzyme mimics

of peroxidase-like catalysis. The produced sensor was tested for detection protein CYFRA

21-1 exhibited good linear response in range 3.9 to 1,000 fg/mL and ultralow LOD of

0.19 fg/mL. The CoZnFeONPs in combination with a disposable µID provided a simple

and efficient biomarker detection method that could satisfy the requirements for a low-

cost and speedy test for early cancer detection.

Apart from it, manganese oxide (MnO) also receives much attention as they feature

outstanding physical and chemical properties, high surface area, tunable size, good

biocompatibility, and stable peroxidase-mimic characteristics. A colorimetric microfluidic

LOC biosensor for rapid and sensitive detection of Salmonella using MnO2 nanoflower

(MnO2 NFs) for amplifying the biological signal, magnetic nanoparticles as recognition

element, and microfluidic chip for conducting automation operation was fabricated as

shown in Figure 5.3 [25]. The colorimetric microfluidic LOC biosensor was integrated

with a convergence-divergence spiral micromixer for sample mixing and incubation. The

colorimetric microfluidic LOC biosensor employed the magnetic nanoparticle (MNPs)

conjugated with antibodies as the Salmonella recognition element and MnO2 NF as the

nanomimetic enzyme in catalyzed the MNPs-Salmonella-MnO2 NFs complex, forming

yellow catalysate. The yellow catalysate was then transported into a detection chamber

and its image was analyzed and processed using the smartphone app to determine the

concentration of Salmonella bacteria. The colorimetric LOC biosensor was able to detect

Salmonella in the range of 4.4 × 10¹ to 4.4 × 10⁶ CFU/mL in 45 min detection time, and

LOD of 44 CFU/mL.

Hao et al. [27] also reported on the detection of Salmonella Typhimurium using

quantum dots (QDs) as fluorescent probes for recognition elements and MnO2 NFs as the

signal amplifier. The proposed detection mechanism is based on MnO2 NFs conjugated

with carboxyl-modified QDs and functionalized with polyclonal antibodies (pAbs) to

form MnO2-QD-pAb-MnO2 NFs complex. The complex flow through the microfluidic

chip and was captured at the detection chamber. In the detection chamber, glutathione

was introduced to dissolve MnO2 on the complexes into Mn²⁺, thus resulting in the re­

lease of QDs. The fluorescent intensity of the released QDs was quantified using the

fluorescent detector to determine the concentration of Salmonella. The sensor exhibited a

linear relationship from 1.0 × 10² to 1.0 × 10⁷ CFU/mL with a low LOD of 43 CFU/mL.

FIGURE 5.3

The schematic image of (a) colorimetric microfluidic LOC biosensor and the proposed mechanism for

Salmonella detection, (b) components and operation flow in the colorimetric microfluidic LOC biosensor for

Salmonella detection. Adapted with permission [ 25]. Copyright (2021) American Chemical Society.

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