Chemistry Reference
In-Depth Information
the optimal conditions has been determined in the range of 20 to 30 nm and surface area is approximately
400 m
2
g
−1
by using BET technology. Thus, the surface area to volume of porous microfluidic chip is
approximate 300 m
2
cm
3
, which is thousands of times more than that of non-porous one. For the optimal
μ
l whole blood at the optimal condition within
15 min, which was approximately two-fold compared with commercial kits. Recently, a SPE microfluidic
device for removing bovine serum albumin (BSA) in which photopolymerized adsorbent as a stationary
phase of SPE was in situ polymerized has been reported [180]. Under the optimal conditions, the adsorption
capacity was 36 mg BSA g
−1
adsorbent.
Liquid/liquid extraction (LLE) is also in the case of cell processing, another alternative method for
extraction and purification. LLE is achieved by contacting fluidic streams at constricted openings between
distinct channels. The approach is attractive since flows can be separated naturally as the channels diverge.
Reddy and Zahn [181] generated dual inlet and three inlet microfluidic systems based on organic- aqueous
liquid (phenol) extraction which could be used purifying DNA directly from cells.
SPE chip, 49.5 ng PCR-amplifiable DNA was extracted per
μ
17.4 Final remarks
The many examples discussed in previous sections of this chapter prove that miniaturization is an active research
field in a variety of application areas. The several attractive features associated to this analytical strategy made
to consider it a valuable alternative when developing more efficient, cheaper and greener analytical methodologies
than those in use in routine and monitoring analyses. It also seems evident that miniaturization should be the
strategy to follow when dealing with the analysis of size-limited samples. However, as shown in previous
sections, the degree of development achieved at present in this field is still strongly dependent on both the level
of miniaturization intended and the nature of the investigated matrix. Really efficient and completely hyphenated
analytical systems are already commercialized for the treatment of aqueous samples with minimum sample and
reagent consumption. On the contrary, the extraction of solid and semi-solid samples remains as an (almost)
unachieved goal. Various examples have illustrated successful strategies allowing the miniaturization of this
step using 'small' versions of the corresponding conventional size technique and different levels of integration
of these treatments with the subsequent purification steps have also been reported as prove of the concept.
However, commercialization of these home-made set-ups is still challenge.
Similar considerations can be done regarding
TAS. Apart of the active research on sensitive detection
principles on microfluidics since the early times of
μ
TAS concept introduction, developments and
improvements of sample preconcentration techniques on microfluidics have been also addressed as second
alternative for the detection of extremely low-concentration analytes. The main proposed approaches have
been microfabricated filtering systems, preconcentration strategies using SPE and electrokinetics and
derivatization schemes.
Although mostly of the selected examples shown in this chapter are really impressive and they have
demonstrated clearly the potency of microfluidics and lab-on-a-chip technology for performing sample
preparation under microscale; however, these approaches are far from being commercial. The possible
reasons could be drawn as follows. Firstly most sample preparation on microfluidics or microchips required
exterior power units which are expensive and huge. Secondly, mostly of the real samples are highly
complicated. Among what is reported above, some microfluidic sample preparation tools are just new ideas
or experimental model, which have not been used for processing real sample. Indeed, the majority of the
reported analytes are a mixture of model fluorescent dyes as LIF detection where the fluorescent derivatization
is consequently also required. Last but not the least, it is not easy for the aimed analyte prepared by
miniaturized sample preparation techniques to be detected by the conventional and commercial method or
technology due to the fact that the present instruments usually requires more target analyte.
μ
